Preference studies of the white‐backed planthopper, Sogatella furcifera (Horvath) (Delphacidae: Homoptera) (WBPH) for different growth stages of rice, Oryza sativa L., indicated that WBPH selected its preferred variety for feeding by alighting on the plant and feeding briefly, ‘tasting’ the plant. Differential preference for shelter, food or oviposition by WBPH were observed for different rice varieties and for different stages of a variety. With the advancement of plant age, rice varieties became more unsuitable for feeding and a process progressing more rapidly in resistant varieties. Most of the resistant varieties viz. Pundia, Landi Sarakanti and Ptb‐33, unsuitable for shelter and feeding were usually not preferred for oviposition. However, the tolerant variety Mahia bankoi, though suitable for shelter and feeding was also not preferred for oviposition. Therefore, when screening varieties by only measuring feeding preference sources having tolerance mechanisms of resistance may be overlooked.

SUMMARYWith a view to examine the effect of pre-sowilag exposure of seeds to gamma radiation (3000 r) on the drought resistance behaviour of barley plants (Hordeum vuIgare L., Var. Kl2), a pot-culture experiment was conducted at a glasshouse attached to the Department of Plant Physiology. The plants were subjected to wilting treatments at tillering stage and were maintained so for ten days. Subsequently, observations on survival capacity, growth behaviour and physiological changes were made during the wilting period. The data obtained were subjected to statistical analysis.Reduetion in soil moisture causes a set-back in the physiological status of barley plants and thereby inhibits the crop growth.Presowing exposure of seeds to gamma-radiation induced drought tolerance in barley plants. It not only improved the growth behaviour but also maintained an active metabolism in plants eren rinder wilting condition.Although the investigation is of preliminary nature, but it certainly of Iers newer scope of research towards useful utilization of gamma radiation in relation to drought tolerance in crops.

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The calcium-dipicolinic acid (Ca-DPA) complex in the spores of Bacillus cereus T is believed to play an important role in the phenomenon of heat resistance. Studies were carried out to determine whether calcium was present in the form of a complex with DPA. Ca and DPA are known to be released into the medium following germination. The presence of Ca-DPA complex in the spores can be established, if Ca and DPA are released in the same ratio in which they are present in the spores. This was studied by preparing spores having different Ca-DPA ratio, and subsequently determining the ratio in which they were released during germination. The present results indicate that the Ca-DPA ratio during the release was the same as in the spores. Attempts were also made by increasing the Zn concentration in the medium to see whether Zn could replace Ca in Ca-DPA complex. The results obtained show that Zn is not taken up by the spores in the presence of Ca.During the life cycle of spore-forming bacteria there are two important stages, sporulation and germination. During sporulation the bacterial cells are transformed into dormant bodies known as endospores. Endospores are highly refractile and resistant to heat and other deleterious agents. Under favourable conditions they can break their dormancy and become sensitive to heat, leading ultimately to the formation of typical bacterial cells. This process is known as spore germination (1-4). Germination can be measured by release of dipicolinic acid (DPA) (5, 6), and increase in UV resistance (7,8) or by decrease in optical density. Germination of bacterial spores occurs in two phases. Loss of DPA and heat stability from the spores form the first phase of germination. During the second phase macromolecular synthesis occurs (9).It is a well-known fact that ions play an important role in spore germination (10). RODE and FOSTER (11) claimed that nonionic compounds such as