Correlation between chiasma frequency and quantitative traits in upland cotton (Gossypium hirsutum L.)

The role of viral infection in inducing variability in virus-free progeny in tomato

The effect of virus-host interactions on subsequent generations is poorly understood. The evaluation of the effects of viral infection on inheritance of quantitative traits in the progeny of infected plants and elucidation of a possible relationship between chiasma frequency in the infected plants and variability of traits in the progeny were investigated. The current study involved genotypes of four intraspecific hybrids of tomato (Solanum lycopersicum L.), their parental forms and two additional cultivars. Used as infection were the tobacco mosaic virus (TMV) and potato virus X (PVX). The consequences of the effect of viral infection were evaluated based on chromosome pairing in diakinesis and/or by examining quantitative and qualitative traits in the progeny of the infected tomato plants. Tomato plants infected with TMV + PVX were found to differ in chiasma frequency per pollen mother cell or per bivalent. Deviations have been observed for genotypes of both F(1) hybrids and cultivars. At the same time, differences in mean values of the traits under study have only been found for progeny populations (F(2)-F(4)) derived from virus-infected F(1) hybrids, but not in the case of progeny of the infected cultivars. The rate of recombinants combining traits of both parents increased significantly (2.22-8.24 times) in progeny populations of hybrids infected with TMV + PVX. The above suggests that the observed effects could be the result of modification of recombination frequencies that can be manifested in heterozygous hybrids and make small contributions to variability in cases of 'homozygous' tomato genotypes (i.e. cultivars).

Features of crossing-over in virus-infected tomato

The evidence of increased crossing over rate in tomato hybrids infected with TAV (Tomato aspermy virus), PVX (Potato virus X), TMV (Tobacco mosaic virus), TMV+PVX indicates the recombinogenic effect of viral infection. Cytological studies of the early diakinesis in healthy and virus-infected tomato revealed significant changes in chiasma number and position. The most significant changes were established for bivalents with two interstitial chiasmata and with one terminal and one interstitial. The data obtained indicate redistribution of the chiasmata position and induction of additional exchanges. The virus-induced recombination is segment-specific and depends on the host plant genotype, virus infection and the interaction between them.

Ecological aspects of the recombination problem

Some consequences of the effect of environmental factors on the recombination system are dealt with in this paper. There are two components involved - the system of individual adaptation (F-system) and the genetic system of population adaptation (R-system). Their interaction offers an optimum interrelation of immediate adaptivity and genetic flexibility within the population. Familiar data on the evolution of recombination control systems are considered in connection with the problems of induced broadening of genotypic variation spectrum with a view to selection.A notion of combined recombination rate and spectrum control is introduced here: disturbance control-due to direct influence of environmental factors on R-system (including meiotic processes), negative feedback control - due to dominance-recessiveness relationship between rec-loci alleles of the "fine" control system, and to the dependence of the R-system on the F-system norms of reaction to environment variation. The problem of dependence of the recombination spectrum on environmental factors has been considered and the hypothesis of a possible mechanism of such a dependence suggested.