QBARS - v26n4 Research - What's New in '72

Research - What's New in '72
August E. Kehr 1
(From Presentation Given at 1972 Annual Meeting, San Francisco)

Geneticist, Plant Science Research Division, Agricultural Research Service, U. S. Department of Agriculture,
Plant Industry Station, Beltsville, Maryland 20705.

As I set about gathering the information to be used in this paper, I got the impression that there has been an increase in the research effort devoted to rhododendrons throughout the country. More and more of our State and Federal workers are giving attention to pressing problems of rhododendrons and azaleas. And such added emphasis in research is justified, because these plants are rapidly increasing in popularity in American landscapes and homes, and today rank as probably the fading flowering landscape crops.

New research accomplishments that I will describe cover nearly all aspects of the Genus. Hence, I will touch on what is new in '72 in plant exploration, evolution, diseases, insects, winter hardiness, weed control, new plants, nutrition. and even damage from air pollution. I sincerely hope there will be something to arouse the interest of everyone here.

In my enthusiasm for some of the research results being presented, if I go overboard and stick out my neck too far, I hope you will accept as explanation an analogy with the turtle; he makes progress only when his neck is cut.


Cylindrocladium Wilt and Blight

A disease which presently is creating serious losses to nurserymen and florists is leaf blight, root rot, or wilt caused by several species of Cylindrocladium. It is a major problem on a national scale - moves around with almost every shipment of azaleas. Dr. Robert Linderman, in our group at Beltsville, has been working on this disease. The organism attacks a wide range of plants, including rhododendrons and azaleas. Frankly, no one knows the full effects on rhododendrons. But it is a real killer on azaleas. The life cycle is most interesting. The leaf phase is the key to spread. In the leaves, sclerotia or black bodies of fungus tissue are formed and these sclerotia in turn produce conidial spores that infect and kill the roots. In fact, the sclerotia act as pumps by producing repeated flushes of conidial spores. The disease is highly dependent on temperature; at 60°F. or below spread is very slow, while at temperatures above 70°F. spread is rapid. Soils may be infested with sclerotia of the organism which cause death of otherwise healthy plants when used as a potting medium. Dr. Linderman has developed some interesting tests that any of us can use to determine if Cylindrocladium is present. It consists of inserting, an azalea leaf in the stem of the affected plant. A second test he calls his "leaf trap technique." Soils infested with Phytophthora wilt organism ( P. cinnamomi ) apparently do not commonly cause any detectable effect on the leaves in which azalea leaves are inserted in soil from around affected plants. If they turn black, Cylindrocladium was present, but if they remain green, the wilt was probably caused by Phytophthora . Hence, the leaf trap technique is a means of distinguishing between wilts caused by Phytophthora and those caused by Cylindrocladium . It also works with rhododendron leaves. Cylindrocladium will also cause flower blight.

Phytophthora Wilt
We have been exceedingly fortunate in developing cooperative research with Drs. Hoitink and Schmitthenner of the Ohio (AES) at Wooster, Ohio, in studies leading to the control of Phytophthora root rot or wilt. Much new information has come from this research.

A most significant finding is that rhododendrons can be infected without showing symptoms. Thus on well drained soils and cool soil conditions, plants may harbor the disease and not show any ill effects whatsoever. But if such seemingly healthy plants are moved or planted in another location where the soil is poorly drained and the soil temperatures rise higher than about 70-75° F., conditions which prevail through most of the East and Midwest, these same plants die from root rot. In a sense, therefore, the misleadingly healthy plants from a favorable location can act as carriers of the disease; they are the Typhoid Marys of the Plant World. The "carriers" appear healthy, but close examination of the feeder roots show browning and killing of the root tips. I am confident that this finding will eventually be one of the critical keys to the control of this universal disease. There may need to be a complete reorientation of handling and production of rhododendrons, possibly even certified disease free plants. There is no effective chemical control of Phytophthora root rots in the soil. The production of healthy plants by strict sanitation in the propagating houses and frames will decrease spread.

The Phytophthora fungus causes damage on many other plants in our gardens including azaleas, Pieris , heather, Kalmia, Arctostaphylos, Cryptomeria, Juniper , and Taxus .

An important phase of the cooperative research in Ohio is the evaluation of rhododendron species and hybrids for resistance to the disease. More than 200 species and hybrids have been tested. Among the more tolerant plants found are 'D. F. Koster,' 'Caroline,' R. racemosum , and R. sidereum . More data on resistant plants will be available in another year or so. When tolerant or resistant plants are identified, the next logical phase will be to use such plants in our breeding programs to develop plants which will tolerate the disease.

Mildew is a common disease, and can do much damage to deciduous azaleas and rhododendron seedlings. Mature rhododendrons appear to be highly resistant and escape any serious damage, but I have lost many seedlings as the result of their being killed by this disease.

There is much genetic resistance in some deciduous azaleas to this disease. For example, the Exbury azalea, 'Persil', is highly resistant, while R. luteum is extremely susceptible. Likewise, very susceptible are R. occidentale and R. forrestii , along with all or most of their hybrids. Most of the eastern azaleas show high levels of resistance, perhaps reflecting natural selection for resistance under eastern conditions where the disease appears to be more serious. An excellent control for mildew is a foliar spray using the systemic fungicide, benomyl. Benomyl, used according to the label, for the first time will enable some of us to grow highly susceptible species and hybrids. Karathane has also been found to be a good control.


Our past President, Dr. Phetteplace, has indicated that some of the insects that attack his choice plants really "bug" him. Undoubtedly, the worst of these insects are the weevils that feed on both the leaves and roots of rhododendrons. There are several species, but the most common are the strawberry root weevil Brachyrhinus ovatus (L.) and the blackvine weevils B. sulcatus (F.) and B. rugostriatus (Goeze), found both on the East Coast and the
West Coast in the cooler regions. The names of these weevils are probably being changed from Brachyrhinus to Otiorhynchus ovatus L. , 0. sulcatus F. and 0. rugostriatus Goeze.

Ages ago, these insects invented women's lib and have succeeded so well in their liberation that no male of the species has ever been found. Generation after generation the race is perpetuated, and the populations increase fantastically without need of male influence of any kind. They are a true race of Amazons, devoid of the privileges of association with the opposite sex. No wonder they "bug" us!

These voracious females feed on the leaves during the summer months, biting characteristic chunks out of the edges of the foliage, thereby riddling the leaves, and rendering them unattractive. What's more, these unmarried matrons hide their shame by feeding only at night. To round out the description it is in true character of their shameful race that they drop their eggs promiscuously as they feed. The eggs fall hit or miss to the ground where they hatch out into larvae that then feed on nearby roots. When the population of larvae in the soil is high, the roots may be almost completely destroyed.

Let us consider controls. Mulches encourage high-surfaced roots and hence plenty of ready food for the very tiny young larvae. Loose sandy soils make for deep rooting and, because larvae cannot penetrate that deeply, they tend to starve. Thus if one can dispense with mulches one key to control is a clean-surfaced soil, and deep soil. The second and most important key to control is to have an insecticide waiting in the soil when the eggs hatch, and before the young larvae can penetrate to feed on the roots. Of utmost importance soil application of the insecticide must be timed to coincide with egg laying. This period usually is about July 1. Chlordane or aldrin sprays on plants and soil surface is good control. Foliar sprays do not effectively control the adults, and the newly hatched larvae must be controlled by the sprays suggested.

Woods weevils cause serious damage to rhododendrons on the West Coast, but are not found on the East Coast. There are two species of woods weevils, the common woods weevil, Nemocestes incomptus (Horn), and the obscure woods weevil, Sciopithes obscurus Horn. Unlike the root weevils, these woods weevils emerge throughout the entire season and males as well as females are present. Because of their different life cycles and characteristics, their control is entirely different. For these beetles foliar sprays of malathion or diazinon applied about monthly during the period late April to Mid-August is the best control.

The so-called Japanese weevil Pseudocneorhinus bifasciatus Roelofs, is a pest on many ornamentals including azaleas and rhododendrons. Adults emerge in June to lay eggs in July to November. Larvae develop in the soil but their damage to roots of living plants has not been established. Adult feeding is far more serious than is that by the blackvine weevil. Japanese weevils are relatively recent immigrants that are widespread from Connecticut to North Carolina and have been found in Indiana. It is controlled by foliar sprays of malathion.

The information on nomenclature and identification of the above beetles was received from Dr. Rose E. Warner, Room W 611, Natural History Building, U. S. Department of Agriculture, Washington, D.C. 20250.

The rhododendron borer, Synanthedon rhododendri Beutenmuller, larva of a clear-winged moth related to the lilac borer Podosesia syringae syringae (Harris), and peachtree borer, Sanninoides exitiosa (Say), is widespread in the U.S. The larvae feed in cambium and sapwood causing dead patches of bark and killing branches. Control - remove loose bark on injured areas and spray with thiodan - monthly intervals in summer. The azalea lace bug, Stephanitis pyrioides Scott, and rhododendron lace bug, Stephanitis rhododendri Horrath, are also widespread. They damage plants in sunny areas and avoid shaded plants - important in selection of planting sites. Control - use malathion sprays. Where available for use on ornamentals, dimethoate is much more effective.

The Florida wax scale, Ceroplastes floridensis Comstock, a large white scale, found in Southeastern United States from Florida to Maryland, is also a recent immigrant. It has one annual generation. Eggs are laid in late May or early June and hatch about 2-3 weeks later (up to 3,000 eggs/female). The young cameo stage nymphs are most interesting.

Spraying with malathion kills crawlers but has to be repeated. Probably the best spray is Sevin which leaves a long lasting residue when applied before hatching. It also kills the young that are up to a month old.

Other insects are a rhododendron aphid, Macrosiphum rhododendri Wilson, which disfigure young growth in Oregon and Washington, and the rhododendron whitefly, Dialeurodes chittendeni Laing, in the same area which weakens plants if the population builds up to large numbers.


Some rhododendrons are difficult to propagate, especially deciduous types. In fact some clones of R. calendulaceum are extremely poor propagators. It would be nice if we had a means of rapid increase of some desirable clone, whether it be a superior form of a species or a new hybrid of great merit. Improved and rapid methods of propagation of rhododendrons are badly needed. I can remember that Dr. Milton Walker, who was instrumental in establishing the Species Foundation, urged research on meristem culture of rhododendrons. As any orchid specialist knows, orchids of some types can be increased a thousand-fold by aseptically cutting the stems in very tiny bits, and from each bit develop another plant identical with the initial plant. Thus in a period of 1 or 2 years, a single plant could be increased to several thousand plants. This technique has never been perfected in rhododendrons, and in fact works only with a few selected orchids.

If true apomixis could be found in rhododendrons, a similar rapid means of increase could follow. Apomixis is the process whereby the seeds of a plant are developed from unfertilized egg cells or maternal tissue, and develop into plants that are essentially clonal propagations of the mother plant. However, despite repeated reports, I do not believe that apomixis occurs in the Genus Rhododendron. I would be extremely happy to be proved wrong, for the discovery of this character could very conceivably be the first step leading to fulfillment of the dream of a rapid means of vegetative propagation in these plants. With the lack of exact data, I believe that all reports of apomixis in rhododendrons to date have been only the result of unplanned parenthood, not apomixis.


If one wants to create a lively discussion in rhododendron circles, he can do so with little effort by bringing up the question of using calcium or lime on these plants. Rhododendrons are usually thought to have a very low calcium requirement, but it now seems probable that the idea is not correct.

Spectrographic analyses of rhododendron leaves from plants in good growth show that the calcium content is 1.22 percent in comparison with a total of 1.74 percent for nitrogen, phosphorus, and potassium combined. 1 Some years ago there was a report which suggested that rhododendron cuttings from stock plants that had received a calcium supplement rooted more readily than did those from untreated plants.

1 Close. E. J. 1957. Gypsum as a rhododendron growth stimulant Plant Propagator 12: 15-16.

There are some interesting research results which bear on the controversy of lime or no lime on rhododendrons, done by a capable scientist in my own shop.

Dr. Denzell Gill of Tifton, Georgia, ran a series of experiments in container-grown plants in which he used calcium sulfate at the rate of 10 pounds per square yard in the soil mix in which azaleas were planted. The soil mix was equal parts Canadian peat moss and sandy loam soil fumigated prior to use.

Calcium sulfate is sometimes called land plaster, gypsum, or sulfate of lime. The results were startling. When calcium sulfate was added, they grew larger and greener in color. Dolomitic limestone or other calcium sources were much less effective sources. Gypsum does not change the pH (acidity) of the soil and is almost insoluble. The reason for the gypsum response is not known. It has been reported that gypsum improves soil drainage and aeration. In Dr. Gill's experiments plants grown in soil mixes that were inoculated with the root-rotting disease organisms, Pythium and Cylindrocladium , escaped the disease if the calcium sulfate was present, but those in other treatments including dolomitic limestone showed symptoms. These results are of interest to growers of all "acid loving" plants - camellias, hollies, etc.

In these tests a loamy sand was used for the potting mix. Different potting mixes may give different responses. Other researchers have not always been able to duplicate Dr. Gill's results on disease control. Despite this, several nurserymen are already using gypsum in their soil mixes.

Yellow Color

Probably nothing has stimulated rhododendron breeding in this country more than the search for bright-yellow-flowered rhododendrons with good plant habits and cultural adaptability. Unfortunately, in this search for the perfect yellow rhododendron, we breeders suffer from lack of a basic understanding of yellow plant pigments. Lacking such information, our efforts are somewhat like shooting white geese in a blinding snowstorm; we know they are there but can't see them and only hope that a lucky shot will achieve our objective.

Fundamentally, there are two distinct types of yellow pigments, the flavanoids and the carotenoids. The flavanoids are water soluble and impart, with the exception of aurones and chalcones, a cream or greenish color in flower petals.

Carotenoids are fat soluble and occur in particulate bodies in the petals. They are all visible to the human eye, and give plant tissues such as carrots their distinctive color.

In breeding for yellow color, we should have a knowledge of the pigments involved. But who can tell us which pigments are present in Crest, or R. lacteum , or R. dichroanthum ? We desperately need this basic information.

At Beltsville the problems of flower pigments are being studied by Drs. Sam Asen and Robert Stewart. For the first time the pieces of the overall puzzle are falling into place. It has been known for some time that metal ions such as aluminum and iron have a profound effect on color. However, recent research by Asen and Stewart that could have tremendous impact is that colors are influenced in their intensity by copigments. Copigments are complex organic plant products which, when present, can intensify some colors. Could such systems operate in rhododendrons and azaleas? Until we have this knowledge, which will become available only from expanded research by plant physiologists and biochemists, we will continue to shoot white geese in a snowstorm.

Plant Exploration
The Will-0-the-Wisp of the Appalachian Mountains

Through the kindness of Dr. Francis Sheild of Newport, Virginia, I learned of a story which may well have the title, Will-O-the-Wisp of the Appalachian Mountains. It is about a report of a bright-yellow-flowered rhododendron growing wild in the Appalachian Mountains of West Virginia. The plant was somewhat like Rhododendron maximum , but with yellow flowers.

This story had its origin in a book by Professor Maurice Brooks entitled "The Appalachians." Professor Brooks has lived his entire life in the Appalachians, and his book reflects his very intimate and keen knowledge of the plant and animal life of the Appalachian Mountain Range which extends from the Gaspe' Peninsula in Canada to Georgia and Alabama. The Appalachians are old in age, having been uplifted prior to the formation of the six continents as we know them today. It is probable that many valuable plant species in these mountains are relicts of past ages.

In a chapter entitled "Something Lost," Professor Brooks outlined conversations with three or more different persons who had discovered and described a rhododendron which in the vernacular of the West Virginia mountains was "yallow, yallow as a cow pumpkin." Professor Brooks definitely found the plant, in fact three of them, although none had flowers nor buds at the time. He took leaf and twig specimens which he sent to various herbaria. These specimens still exist and can be examined by anyone who doubts the story. This slide will lend assurance that the herbarium specimens vary from eastern native rhododendrons including R. maximum.

A group of us, along with Professor Brooks, visited the area in June 1971, but failed to find the plant. Professor Brooks had not been there for 30 years, and the wooded area where the plant existed had been cleared of all woody plants, and no trace could be found of the original plantings. We are, therefore, left with these intriguing, but presumably accurate, facts:

  • A yellow-flowered, large-leaved plant was reported in the area by several different persons in the 1930's.

  • Professor Brooks, who is an excellent plantsman, saw the plant when not in flower and identified it as a large-leaved Rhododendron species or hybrid.

  • Herbarium specimens of the plant are available for study today.

These inconclusive facts whet our interest but fail to satisfy the thirst for the exact knowledge we would like to have about this elusive plant; how it originated, and especially whether similar plants exist today in the thousands of square miles of wild, wild hills of Pocahontas County, West Virginia. These are questions that must go without answers for the present, and perhaps forever.

Weed Research

An important breakthrough in weed control occurred in recent months-a specific control for nutgrass or nut sedge. An experimental chemical, a product of the Minnesota Mining and Manufacturing Company, 1 offers the first effective control of this serious weed.

1 Use of a Company or Product name by the Department does no: imply approval or recommendation of the product to the exclusion of others which may also be suitable.

Nutgrass, both northern and southern types, is so named because it forms underground enlarged roots that are somewhat nut-like roots under the name "ground almond." As a boy, I purchased some of these "ground almonds" as a curiosity. They were all they were claimed to be - and more. We eventually had to move our home garden because nutgrass took it over. It was my first experience in plant introduction.

Origin and Evolution of Rhododendrons

The origin and evolution of plants has always been a fascinating subject to me. Consequently, I have become interested in the work of Dr. E. E. Leppik at Beltsville on the origin of rhododendrons. And the origin of rhododendrons apparently goes back at least 60 millions of years and is tied into the origin of the six continents themselves. It's a beautiful story, a story that only 5 or so years ago would have been considered science fiction. I will jump right into the story without attempting to present the increasing volume of evidence that substantiates the theory being presented. I would be way out of my field if I attempted to do so.

The theory currently being advanced is that 255 million years ago the six continents made up a single land mass, called Pangaea. Because of the drifting of the relatively thin Earth's crust, Pangaea divided into two definite super continents called Laurasia in the North and Gondwana in the South. This break occurred in Triassic about 200 million years ago. This date is important because the first ancestral species of the Genus Rhododendron evolved after this break. Age-wise rhododendrons are therefore relatively young when compared to many other plants in today's world. The evidence for this origin of rhododendrons arises from the fact that almost without exception rhododendrons are native only on the continents on North America, Europe, and Asia, or in other words the super continent of Laurasia. The newly evolved plants were prevented from moving to the Southern continents by the widening body of water.

There is more evidence for this theory. The fir rust, Chrysomyxa , which you have all heard discussed at earlier annual meetings by Dr. Charles Gould of Puyallup, Washington, is a disease of spruce trees. But to complete an essential part of its life cycle, the fungus must live on certain species of Rhododendron . In brief, if there are no rhododendrons present, the fungus cannot survive. Ancestral forms of conifer trees developed prior to rhododendrons, during the period when there was a single land mass. Consequently, today the descendants of their common ancestors occur on all six continents. But spruce rust today occurs only in Eurasia and North America which were until the Tertiary period united into Laurasia, and has a common range with the distribution of spruce and rhododendrons. Hence, spruce trees, the spruce fungus, and rhododendrons could only have evolved in close association after Laurasia was already separated from Gondwanaland, but while North America was still connected with Eurasia. Thus rhododendrons first appeared on Earth sometime after 200 million years ago but before 165 million years ago when North America separated from Eurasia. Rhododendrons are thus a young genus, and as such, are still undergoing rapid evolution. Perhaps this fact accounts for the large number of species and species variants which occur in nature.

Air Pollution

On the slide being shown is a condition that few here will identify correctly. The two plants are the same variety, were originally the same size, and the same age, and had exactly the same care and culture. The only difference is that the smaller plant was grown in a greenhouse in which the air came from the usual supply of air normally found around Beltsville, Maryland, while the larger plant was grown in a greenhouse in which the air was filtered before entering the greenhouse. It is apparent that rhododendrons suffer chronic damage from air pollution, although they show little or no visual effects.

Air pollution may thus contribute to some of the poor behavior of these plants in urban areas. Rhododendrons are classified as tolerant species to sulfur dioxide and ozone. These air pollutants inhibit photosynthesis in their long term effects, and thus result in reduced growth. Air pollution on rhododendrons, however, is not considered a major problem at this time.

Winter Hardiness

Winter hardiness is essential for rhododendrons and azaleas in most parts of the U. S. The factors which control winter hardiness are among the least understood bits of knowledge in today's horticultural world. I would like to discuss some recent work at Michigan State that has shed some light on this vital subject for evergreen azaleas. 1

1 G. P. Lumis, R. A. Mecklenburg and K. C. Sink. 1972. Factors influencing winter hardiness of flower buds and stems of evergren azalas. J. Amer. Soc. Hort. Sc. 97(1): 124127.

In these studies two azalea clones were evaluated for hardiness during two winters. One clone was R. poukhanense , which is considered by many as one of the hardiest of the evergreen types. The other clone was 'Maryann,' a Gable hybrid with 25 percent poukhanense germ plasm, 25 percent kaempferi germ plasm, and 50 percent indicum germ plasm. Hardiness was studied both outside under natural conditions and inside under carefully controlled conditions. The results were interesting and somewhat surprising.

At temperatures of -20° C. (-4° F.) the average bud loss for R. poukhanense was 91 percent, while for 'Maryann' it was less than 19 percent. Thus in these studies 'Maryann' was considerably hardier than R. poukhanense . The chief difference between the two varieties was the percentage of water in the apical stems, R. poukhanense stems had 54 percent moisture, 'Maryann' stems 49 percent. When stems of R. poukhanense were allowed to dry down to 46 percent, they could survive at a lower temperature.

Frozen twigs of R. poukhanense contained large ice masses in the tissues, while 'Maryann' had no large ice masses. Likewise, R. poukhanense tissues showed extensive splitting of stem tissue while 'Maryann' stems had no large splits.

Hence the difference in winter survival of the two clones was solely a function of the amount of water in the stem tissues.

What should this mean to those of us interested in hardy azaleas and rhododendrons?

To those interested in breeding for winter hardiness, we have a measurable factor to evaluate seedlings. We must determine and select those genetic lines with low water content. Selection for a lower and lower water content of dormant, conditioned plants would provide an objective and easy means of selecting for increased winter hardiness.

What's New in New Plants

We all get excited by the discovery of interesting new rhododendrons. I have selected 10 such plants that have been very exciting to me and which are not generally well known.

1. 'Mahogany Red'.  Mr. Wada has found a single plant of R. mucronulatum growing in Japan in the wild with deep purplish-red flowers instead of the usual lavender or pink. He has named this clone 'Mahogany Red.' It represents a unique variant in that it contains about 2-3 times the pigment content of the type form.

2. A prostrate form of R. keiskei . Warren Berg and Frank Doleshy were most astute in recently collecting on the Island of Yakushima a form of R. keiskei that is almost completely prostrate in its growing habit. This form is very distinct from all other forms of R. keiskei known to date. It has created such excitement that it already has brought about an acute rash of new nomenclature. Consequently, this new form is variously called:

  • R. keiskei var. prostratum by many in the U. S.

  • R. keiskei var. cordifolia in Japan.

  • R. laticostum , an entirely new species by Collingwood Ingram in England.

3. A distinct variety of R. catawbiense . In general R. catawbiense is native to the southern Appalachian Mountains at elevations of 4,0005,000 feet where it enjoys a very cool climate. Recently research done by members of the Azalea Chapter has found isolated colonies, probably relict clones from the ancient past, which are growing at elevations only 200-300 feet above sea level in North Carolina and Georgia. These clones, named R. catawbiense var. insularis grow where they survive extremely high summer temperatures, and offer valuable germ plasm for those persons developing heat resistant types.

4 . A new yellow species or hybrid. Among the seed received from Forrest under collection number 16684 was a yellow and orange-flowered plant which has never been damaged by wind or frost in Denmark. This plant, named R. selense affinis is rather near R. crythrocalyx and R. esetulosum , but Davidian says it is neither of these species. It was collected near Beima Shan in China, and for this reason is being called R. exbeima . I am not sure of the official status of this name however.

5. A bright yellow form of R. hanceanum . Last year in Scotland it was my privilege to see a bright-yellowed flowered form of R. hanceanum . It is conceivable that this is the same form Brian Mulligan saw in Ireland several years ago. In any event this plant has now been established in this country. Hybrids of this yellow R. hanceanum and R. ludlowii are among the most beautiful, low-growing yellow hybrids I have ever seen.

6. A new subspecies of R. brachycarpum . I have recently assisted in the preparation of a manuscript describing a subspecies of R. brachycarpum , named by the author, Dr. Tor Nitzelius of the Goteberg Arboretum in Sweden, as subspecies tigerstedtii . This subspecies from Korea is larger-leaved, larger-flowered, and earlier by 2 weeks than the Japanese forms of R. brachycarpum . But more significant than all this is that these plants survive without harm outside, and unprotected by snow, at temperatures of nearly 50° below zero F. at Mustila Arboretum in Southern Finland, which is on about the same latitude as the northern part of Labrador and Anchorage, Alaska. To those interested in breeding for cold hardiness, these plants offer germ plasm which may be more valuable for developing cold tolerance than anything previously known in our nonscaly types, including R. catawbiense , which has limitations as a parent in breeding pure colors because of the gene for purple color that it carries. It is a credit to Mrs. Esther Berry and her unique seed exchange that this germ plasm is already being grown by persons throughout the U.S., distributed in 1971 as number 30, from seed supplied by Britt Smith. Maybe some people present were farsighted and lucky enough to request this seed. If so, guard the plants for they offer great promise for developing fine-foliaged, good-colored, hardy hybrids in the future.  Perhaps it is in order to say again, I have said many times before, that the ARS Seed Exchange will have more beneficial effect on the future of Rhododendrons in this country than any other single activity of the Society.

7. New Rhododendron at the 1971 Chelsea Show in London and from Scotland.  A new hybrid which received honors at the 1971 Chelsea Flower Show was Rh 'Stanway,' a cross of R. fortunei x R. 'Jalisco.' It has fine yellow-colored flowers, of good size and quality. It points up the use of R. 'Jalisco' as a good parent in breeding for yellow hybrids. Some new plants from the Cox and Hutchinson Expedition include a new species in the Ciliicalyx series, and a rare species R. santapavii.

8. A new heat tolerant species.  In a recent visit Dr. Peter Valder of the Department of Botany, University of Sydney, N.S.W., told me he had noticed a rhododendron growing in a neglected garden which normally would be too hot for rhododendrons. Upon investigation he found the plant to be R. simiarum , formerly R. fordii , a native of Hong Kong and Southeast China. In view of the hot conditions under which this species is continuing to survive, it must be concluded it has the toughness needed for survival under hot weather conditions. Consequently, it offers an untapped source of germ plasm in breeding programs. We understand that R. hyperythrum from Taiwan also possesses high levels of heat tolerance.

9. A red form of R. augustinii . A red form of R. augustinii really is not new. It has only been overlooked. About 5 years ago Dr. Serbin showed me a plant of this rare variant which he had obtained in England. I saw another plant last year in Scotland. The flowers are truly red, and the plants no doubt originated from the 1924-25 Forrest Collection, Number 25914, in North Yunnan Province.

10. R. sidereum , a source of root rot tolerant plants.  Although I have mentioned this discovery earlier, it is of sufficient importance to bear repetition, along with a word of caution. The plants of R. sidereum tested by Drs. Hoitink and Schmitthenner were found to be highly tolerant to Phytophthora root rot, even after three to four inoculations. This fact alone will make this species of interest for breeding for root rot resistance, or looking for tolerant root stocks for grafting. It must be pointed out that species in general vary considerably and it does not follow that all plants assigned to the species R. sidereum are similarly root rot tolerant. After all, all of us in this room belong to the same species, and just look at the variations that exist just within this small segment of the human population. Similar variations occur among individuals of any species population.

New Research Facility Being Planned Probably foremost in a discussion of what's new is a mention of the new USDA laboratory and green house facilities which are about to be built at Corvallis, Oregon, and Puyallup, Washington, for the purpose of research on ornamental plants, including rhododendrons. This new research will include programs on disease control, culture and breeding of improved ornamental plants. It is projected that when fully staffed, a total of four scientists-a plant breeder, two plant pathologists, and a physiologist-will be located at Corvallis and one physiologist at Puyallup. The new research program will be aimed at solving problems now facing the nurserymen and florists in the Pacific Northwest. Construction of the buildings to house the scientists will soon be getting under way.


Although there appears to be increased research activity involving rhododendrons and azaleas, present research programs are not adequate to meet the present problems and needs.

Among the many needs facing us are:

(a) Insects continue to cause severe damage to rhododendrons and azaleas. With the present restrictions on use of some insecticides, insects are uncontrolled in some areas. Much research is needed to develop alternate controls, including biological controls, and breeding for resistance to insects.

(b) Root rots especially caused by Phytophthora and Cylindrocladium are the most damaging diseases of rhododendrons and azaleas. Controls are needed, especially biological controls and development of resistant varieties.

(c) Improved propagation methods are needed, especially in deciduous azaleas. New methods, such as meristem culture and tissue culture need to be worked out. Basic information on propagation needs to be developed.

(d) A very limited number of azalea and rhododendron cultivars have been developed that are suitable for pot culture as florist crops, or landscape types, hardy enough for growing in extreme northern areas, or to withstand alkaline conditions of the Midwest. A broad program of improvement is urgently needed to meet urban conditions. Heat tolerant cultivars are needed to extend the range of adaptability of these plants.

(e) Cultural improvements in these crops are essential including chemical pruning, fertilization, weed control, mulches, soil media, and many other problems.

(f) Evaluation of present day cultivars needs to be done systematically throughout the country, and official test gardens comparable to the rose test gardens need to be established.

(g) Many of our bulletins and leaflets prepared by Federal and State agencies need updating. Much of the information in present editions is out of date. New publications are urgently needed, especially to provide information for the Midwest and South.

(h) The nature and control of pigmentation in relation to flower color is not well enough understood so that the information can be applied to plant improvement.

(i) The nomenclature in rhododendrons badly needs clarification. We have many synonyms that cause confusion in plant identification. Likewise, the chromosome numbers of many species and hybrids are unknown, and lack of knowledge makes breeding and genetic research inexact.

(j) Mainland China is a rich source of germ plasm and there is need to develop plant exploration to that country.

(k) More information is needed on soil-water relationships for rhododendrons, as well as on nutrition and fertilizer requirements.


Although I have taken nearly 60 minutes telling you "Research: What's New in '72", I can summarize the present state of our knowledge about rhododendrons, and all other plants for that matter, in a single sentence, as follows:  "What we know about plants today is merely a drop in the bucket compared to what we do not know."