An evaluation of seed and seedling drought tolerance screening tests in wheat

Summary A series of experiments was performed in order to evaluate the significance of seed germination and seedling growth in osmotic media as screening methods for drought tolerance.Ten spring wheat (Triticum aestivum L. em Thell.) and one durum wheat (Triticum durum Desf.) were tested under controlled environments, using polyethylene glycol-6000 (PEG) solutions as the moisture stress inducing media.Tolerance in the rate of endosperm utilization, under stress, prior to the onset of germination varied among cultivars.Germination rate or injury to germination at various concentrations of PEG differed significantly among cultivars. Cultivar rating with respect to injury to germination changed with stress levels. Injury to germination did not correlate with endosperm utilization rate in PEG or in water.Germinating seedlings were tolerant to extreme desiccation up to the stage of emergence of the first leaf from the coleoptile.Growth of photosynthesizing seedlings was monitored as they were carried through an increasing concentration gradient of PEG solutions, ranging from –5.9 to –11.3 bars of water potential. Cultivars significantly differed in seedling growth tolerance to increasing levels of water stress. Seedling growth tolerance across cultivars was not correlated with their germination responses under srress.It is concluded that tolerance to water stress in growing seedlings can be screened for by using PEG-containing nutrient solutions. It can not be predicted from germination tests in osmotica.Work was done under a US-Israel Binational Science Foundation (BSF) Grant no. 1654/78.Contribution from Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 192-E, 1979 series.     

Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 7. The inheritance of resistance and bitterness and the relation between these characters

Summary The inheritance of resistance to the twospotted spider mite and of bitterness in cucumber has been studied in three sets of P₁, P₂, F₁, F₂, B₁₁ and B₁₂ of crosses between three bitter, resistant lines and one non-bitter, susceptible line. Resistance to the twospotted spider mite as measured by acceptance and oviposition appeared to be determined by several to many genes, which are inherited mainly in an additive fashion. Bitterness is basically governed by the gene Bi, which, contrary to earlier reports, is inherited in an intermediary way, while the expression of Bi is influenced by additively inherited intensifier genes. Whereas Bi and the bitterness intensifier genes are not related to the resistance factors acceptance and oviposition, they are related to resistance or tolerance as measured by the damage index. This relation is explained by linkage rather than by identity of the genes concerned. Changes in the test methods and breeding consequences are discussed.