Tolerance of Lolium hybrids to quantitative variation in nuclear DNA

Abstract

THE genus Lolium contains six species, all diploids with 14 chromosomes. The chromosomes of the inbreeding species are larger than those of the outbreeders and carry about 30% more DNA¹. Although the range of variation in nuclear DNA amount is not large, in comparison with other genera of flowering plants², Lolium is exceptional in that crosses between diploid species with widely different amounts of DNA produce F₁ hybrids which set viable seed on backcrossing or, alternatively, by intercrossing to produce F₂s. Segregation of nuclear DNA amount among hybrid derivatives by independent chromosome assortment and crossing over at meiosis in the F₁ makes feasible a genetic assay of the effects of the differential interspecific DNA component. This report describes the segregation of nuclear DNA amounts among F₂ progenies (seedlings 5–7 d old) from F₂ hybrids between L. temulentum with high DNA and L. rigidum with low DNA content. F₁ seeds were obtained by allowing the F₁ hybrids to intercross in isolation from foreign pollen. From the DNA distribution in F₂ it is possible to draw conclusions about the influence of the differential DNA component on gamete and zygote viability. The results are given in Fig. 1.