THE INFLUENCE OF TILLETIA TRITICI (BJERK.) WINT. AND TILLETIA LAEVIS KÜHN ON THE GROWTH OF CERTAIN WHEAT VARIETIES
Authors: SAMPSON KATHLEEN , DAVIES D. WALTERS 
Published: February 2008

Summarising the results of the experiments described in the present paper, it is evident that bunt has a distinct influence on vegetative organs of the plant in addition to the well‐known effect on the grain. Both species which cause bunt, Tilletia tritici and T. laevis, were included in one experiment only, from which it appears that the influence of the latter species, while tending hi the same direction, was distinctly weaker in its effect than T. tritici. This conclusion is in harmony with the results of other workers (4,10, 11).

The following conclusions refer to T. tritici, with which speck the work was mainly carried out:

Soil germination and establishment.

The actual percentage of germination has not been found. to differ appreciably in bunt‐free and bunt‐contaminated samples, but in one experiment a considerable difference was manifest in the final establishment, the bunt‐free samples showing an increase of 25–37 per cent, when compared with those which were contaminated with spores before sowing (Table I). The greatest difference (37 per cent.) was shown by the variety Browick, which gave the lowest establishment figure and had presumably suffered most intensely from the unfavourable climatic conditions.

Early growth.

The first visible symptoms of a retarding influence on growth are not always manifest at the same stage of development in the wheat plant. Under one set of conditions (p. 92) the effect was clearly shown by plants in the seedling stage, since those derived from bunt‐contaminated seed differed from the control by 14–17 per cent. in height, and 16–20 per cent. in the dry weight of 100 shoots. In another experiment (p. 97) where a considerable reduction in height was evident at maturity the plants showed no appreciable effect during the first ten weeks of growth.

Tillering.

In the matter of tillering the influence of the fungus was in the opposite direction to that recorded for growth in height, bunted plants at the period of maximum tiller development producing in one experiment 16 per cent. more tillers than healthy plants grown under precisely the same conditions. At maturity in both cases the number of heads was considerably less than the total number of tillers produced, but bunted plants still showed an increase over those that were healthy (Experiments III and IV).

A similar difference was noted in the case of plants grown in rows in the field1.

Length of straw at maturity.

A reduction in the length of straw appears to be one of the most constant results of the influence of the fungus on vegetative growth. It will no doubt be shown that the degree of reduction varies with the variety, the season and possibly with the origin of the spores used for contamination. In the experiments here described a reduction in height amounting to 16–19 per cent. in the case of Hen Gymro and 13 per cent, in the case of April Bearded was recorded. It was shown moreover that the reduction was considerably greater in the case of tillers carrying heads in which every grain was bunted than in the case of those bearing both healthy and bunted grain.

Length of ripe ear.

In the case of Hen Gymro wheat the fungus showed a slight retards effect on the length of the ear, while in the variety April Bearded the bunted ears were, if anything, slightly longer than the normal. More data are desirable on this point, since the influence on this organ is probably largely determined by the morphology of the ear in any particular variety. It appears to be generally recognised that ears of the compactum type are abnormally narrow and long when bearing bunted grain (6,15). Plate VII shows bunted and normal ears of T. vulgare var. Standard Red, which possesses normally relatively wide, dense ears. For comparison are shown healthy and diseased heads of Hen Gymro, which has ears characteristically lax.

Root development.

In one experiment where data were obtained on the dry weight per 100 plants of the roots at maturity a significant difference was apparent between bunted and healthy specimens, the former showing a decrease of 22 per cent.

From the practical point of view, where the final yield of healthy grain is of primary consideration, the most important aspect of the question, apart from the effect on the grain itself, is probably the influence of the disease on establishment and early growth. It is of come recognised that any check which the plant receives in the early stages of growth will be exaggerated later in the case of plants placed in competition with healthy individuals, as must happen in a partially bunted field crop. The full extent of the retarding influence on growth was possibly not exhibited in certain of the experiments under review since the bunted plants were not seriously subject to competition.

Since it has been shown that the presence of the parasite tends to increase tillering, the reduction in heads at harvest which was a striking feature of previous treatment experiments must be attributed either to the stimulating effect of the chemical used for treated lots, or to the depressing influence of bunt on establishment in the field. From the data here given the second alternative seems the more feasible, but since the Muence of bunt on establishment is, perhaps more than any other, reply to be affected by seasonal conditions and to differ with the variety and the origin of the seed, it is desirable to obtain further data on this of the problem, using a large number of seed samples and varieties and a wide range of environmental conditions.