Vegetative Proliferation of Grasses and Phyllody of Clovers

BOTANICAL EXCURSIONS IN EAST SUFFOLK

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as Bawdsey Manor and the plantations did not exist. Traces of these dunes persisted in one small area on the face of the cliff, and were visible up to recent times before this place was enclosed.

Sea Sandwort (Honkenya peploides), Lyme-grass (Elymus arenarius) and Marram (Ammophila arenaria) occurred there in recent years, but Sea Holly (Eryngium maritimum) and Prickly Salt-wort (Salsola kalt) had become extinct at this spot, although both can still be found less than a mile away near the Ferry.

VEGETATIVE PROLIFERATION OF GRASSES AND PHYLLODY OF CLOVERS By

P. J.

O.

TRIST

PROLIFERATION in grasses has been observed at least since the time of Linnaeus and many reports and experiments have been published. Langer and Ryle, (1958) have not only clarified the former confusion in the distinction of conflicting terms which have been used under the general heading of proliferation, but have determined the cause of proliferation.

In " vegetative proliferation ", i.e., where there is vegetative growth from a floret in the absence of a seed, two reasons have to be considered. In some species of grass, vegetative proliferation is genetically determined as in Festuca vivipara Sm., and Poaalpina L. var. vivipara. In others, the cause of proliferation is now shown to be due to insufficient exposure to the hours of daylight required by a species to enable it to effect fĂźll ear formation.

As a distinction between vegetative proliferation and vivipary, it was suggested by Arber (1934) that the latter should be referred to as true vivipary, where the seed germinates whilst still attached to the parent plant.

Most observations on grass proliferation have been made late in the season. In the autumn of 1958 and 1959, several observations were recorded in Suffolk of proliferations on Dactylis glomerata L., Cynosurus cristatus L. andLoliumperenne L. Records show that proliferation is also recorded for Agropyron repens Beauv, Alopecurus pratensis L., Arrhenatherum elatius L., Festuca rubra L., Phleum pratense L., Poa trivialis L. and Deschampsia caespitosa Beauv.

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In their vvork, Langer and Ryle selected Phleum pratense (Timothy S.48) and tested the effects of exposure to long and short day treatments on flower production.

T h e experiment started when the length of day was sufficient for flower production to occur in Timothy. At first all plants were exposed to fĂźll daylight hours. After 2 weeks, some were reduced to short day exposure and others were returned to short days after 3, 4 and 5 weeks in long day exposure. Some plants continuously remained in natural long days and control plants in a short day allowance of 8 hours. After 7 weeks, all plants were given long day exposure. After 6 weeks, the long day group produced numerous normal flower heads. In other groups, head emergence was delayed and plants only allowed 2, 3 and 4 weeks of long day treatment produced few heads on a twisted rachis and later showed proliferation with single leaf-like structures.

An examination of the floret showed that with the exception of the leaf-like structure, all other parts were normal and the leaf was an elongated lemma bearing a ligule. At a later stage, this leaf-structure exserted three leaves, and a further three in various stages of development were found by dissection : following these developments the floral parts atrophied. T h e continued observations in this experiment showed that the previous consideration of types of proliferations are only stages in the development of proliferation.

Thus, except where proliferation is genetically determined, as in Festuca vivipara, other grasses which are found flowering late in their season and exhibiting proliferous growth, should not be recorded as "proliferous f o r m s " . They must be regarded as plants which are unlikely to set seed and which produce abnormal leaf structures, due to ear emergence at a time of year when there are insufficient daylight hours for normal ear production. This minimum daylight requirement varies in the grass species.

PHYLLODY.

Proliferous growth in clovers has also been observed for a number of years and the condition has been regarded as a physiological abnormality and not due to environment or other causes.

Trifolium repens, and the varieties S.100 and Kersey White, have exhibited proliferous growth. Recent research has shown that this type of proliferation is caused by two viruses which produce different forms of abnormal growth and other characteristics.

For some time the term proliferation has been indiscriminately used to describe proliferous growth in both grasses and clovers, regardless of the origin or cause of the proliferation. It has now

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been shown that abnormalities in the head and other parts of the clover plant are due to virus infections. This condition is known as phyllody and is not related to the causes previously described and which give rise to proliferous growth in certain grasses, known as proliferation.

The work carried out by Frazier and Posnette (1957) has not only clarified the cause of this clover condition, but has verified the source of the infection, and the cause of hitherto unexplained conditions of strawberries, known as Green-Petal and Bronze Leaf. These two conditions are the result of virus infections and are carried by leaf hoppers from the strawberry to clover plants and give rise to abnormal growth in the flower heads and in other parts of the plant.

Frazier and Posnette have determined two strawberry diseases which have previously been grouped under the name of GreenPetal :— (a)

Green-Petal caused by the virus inducing phyllody in clover, and

(b)

Bronze Leaf wilt caused by the clover Witches' Broom virus.

The workers record that crimson, red and white clovers can be infected, and have described three Symptom categories :— (i)

Witches' Broom : " Severely stunted plants: young leaves chlorotic, especially at the margins and unfolding delayed as in club leaf (Black 1944) ; old leaves usually bronzed ; extreme proliferation of crown and axillary buds ; inflorescence usually small; flowers normal in structure, but pale and often opening irregularly; no phyllody."

(n)

Phyllody : " Plants only slightly stunted ; vein chlorosis old leaves slightly bronzed ; slight crown proliferation phyllody affecting most or all of the flowers in the inflorescence."

(iii) " Plants with symptoms of both Witches' phyllody of the flowers."

Broom and

This report also records that the phyllody virus infection has also been found on Anthemis cotula, Erodium cicutarium, Anagallis arvensis, Solanum tuberosum, Callistephus chinensis and Helenium Sp. ; the following also being infected with the Witches' Broom virus : Dauern carota, Plantago major, Solanum tuberosum, Anthemis cotula and Lycopersicon esculentum.

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Another condition found on White Clover is recorded by Carr (1959) and is termed " Red Leaf " and " not yet shown definitely to be of virus origin, causes marked bronzing of the leaves, together with pronounced loss of vigour, so that affected plants tend to die out, especially during the winter."

The phyllody virus infection was found in every one of the twenty-three crops surveyed by Carr. The intensity of infection ranged from 0.1% to 10%, with one crop of 14% infection.

The survey results indicate that the disease was not less frequent in areas remote from the main seed growing districts. Investigation for phyllody in Red Clover was not extensively carried out, but a careful examination was made of one field adjacent to a crop, of S.100 White Clover with a 3.3 % infection and no phyllody could be found.

The " R e d Leaf" condition was found in every crop surveyed, except one. Carr also found that where phyllody was frequent or severe, Red Leaf was also present and suggests that phyllody and Red Leaf are transmitted by the same vector.

REFERENCES.

Arber, A. (1934).

The Gramineae. A study of cereal, bamboo and grass.

Cambs. Univ. Press.

Black, L. M. (1944).

Some viruses transmitted by Agallian leafhoppers.

Proc. Amer. Phil. Soc. 88, 132.

Carr, A. J. H. (1959).

Survey of White Clover seed crops for virus diseases in the N.A.A.S. Eastern Region.

Private communication.

Frazier, N. W., and Posnette, A. F. (1957).

Transmission and host ränge studies of Strawberry GreenPetal Virus.

Annais of Applied Biology, Vol. 45.

Langer, R. H. M., and Ryle, G. J. A. (1958).

Vegetative proliferations in herbage grasses.

Jo. Brit. Grassland Soc., Vol. 13, 29.

30th March, 1960.