Molecular heterosis for heat-sensitive enzyme alleles

Heat denaturation studies were carried out and revealed hidden genic variants with the same net charge at the Octanol dehydrogenase-1 locus in Drosophila pseudoobscura. Studies of several genetic crosses between strains with different heat-sensitivity alleles showed that the F(1) retained more in vitro enzyme activity after being heat-treated for a specified amount of time at a given temperature than the heat-resistant parent. We call this phenomenon "heterosis for heat-stability of enzyme activity" and discuss its possible molecular mechanism, its relation to maintenance of genetic variation in natural populations, and its bearing on the "classical" and "balance" hypotheses.

Population biology of Avena : II. Isoenzyme polymorphisms in populations of the Mediterranean region and Central California

Surveys for polymorphisms in natural populations of A. barbata sampled in California grasslands had provided evidence for widespread monomorphism and rather localized polymorphic areas in the north coastal and San Francisco regions, based on a set of morphological and isoenzymatic marker loci. Since this species, like many other annuals, was introduced from the Mediterranean region during the Spanish mission period, a comparative study of the Canadian-Welsh collections of Avena species from the Mediterranean region was undertaken using various plant characters and starch gel electrophoresis to analyze variants for esterase, phosphatase and peroxidase systems. A total of 96 samples including 73 of A. barbata and 23 of A. hirtula were studied and the results were scored to compute the polymorphism indices. In both species, only 10 to 15 percent sites showed any significant degree of polymorphism of which a majority seemed to originate from localized regions in Italy and Turkey; a part of this observed lack of within-sample variation might be the result of small sample size. In general, the patterns of variation in A. barbata from the California surveys and the present analyses seemed to be very similar and raised some interesting questions on (a) the colonizing history of introduced materials (b) the factors underlying such marked patterns of geographical variation, and (c) the current evolutionary changes occurring in these two broad, disjunct areas of species distribution.

Population dynamics of Pythium aphanidermatum in oil cake amended soils

Experiments were carried out to determine the effect of decomposition of oil cakes, used as organic manures in India, on the population of Pythium aphanider-matum in soil. Low quantities (0.1 to 1.0% w/w) of castor and peanut cakes stimulated the growth of the fungus at 20° to 30 °C but in presence of higher quantities of these cakes the growth of the fungus in soil was inhibited. Inhibition was more conspicuous and was caused by lesser amounts of these cakes at high temperatures than at low temperatures. On the other hand, margosa cake (Azadirachta indica) was highly stimulatory to the fungus in all concentrations of 0.1 to 5% at 20°–30 °C, but caused inhibition at 36 °C. Washing of margosa cake with alcohol made it as inhibitory as the other two cakes. It has been suggested that the three cakes affected P. aphanidermatum in soil differently because of their chemical nature and the nature of their decomposition products which may (i) directly suppress the fungus through toxic effect, (ii) stimulate it through nutritional effect, (iii) stimulate or inhibit actinomycetes lytic to the pathogen. Temperature and pH of soil during.decomposition, as well as C:N ratio of the cakes, do not play any major role in the suppression of the fungus.