Recurrent selection progress in a population derived from an interspecific peanut cross
SummaryTwo cycles of recurrent selection for yield were previously conducted using a population of Arachis hypogaea L.-like tetraploid hybrid derivatives selected from among the progeny of a cross between A. hypogaea and A. cardenasii Krap. et Greg. nom. nud., a diploid species with resistance to late leafspot (Cercosporidium personatum (Burk. and Curt.) Deighton). Using the 10 highest yielding parents from each of the above cycles of recurrent selection, a study was conducted for 12 morphological traits and susceptibility to leafspot infection in a replicated test at a single location. The two parents used to initiate the interspecific hybrid population (PI 261942-3 and A. cardenasii) as well as two adapted cultivars (Florigiant and NC 7) were included as checks. The objectives of the study were to determine the amount of genetic variation remaining in the population after two cycles of recurrent selection in order to predict whether further progress from selection could be expected and determine the potential for utilizing wild species for the improvement of quantitative traits in peanut. The results indicate that significant levels of genetic variation remain in the population after two cycles of recurrent selection for all traits measured, including several components of yield and leafspot resistance. This suggests that continued progress in population improvement from further cycles of selection should be possible while enhancing the genetic diversity of cultivated peanut germplasm.
Variation in progenies of an Arachis hypogaea x diploid wild species hybrid
SummaryDerivatives of a cross between cultivated peanuts, Arachis hypogaea L. (2n=40), and the wild species collection GKP 10017 (2n=20) were compared morphologically, for leafspot resistance and for yield. The objective of the study was to determine the effects of wild species germplasm on the A. hypogaea genome. The sterile F1 hybrid which resulted from crossing the two species was treated with colchicine to restore fertility at the 6x ploidy level. The resulting hexaploid was cytologically unstable and progeny lost chromosomes until stability was regained at the 2n=40 chromosome level. Forty-seven characters were used to analyze the variation among plants in the tetraploid interspecific hybrid population. The plants were compared to four cultivated lines plus GKP 10017. Many hybrids were intermediate to the two parents in morphology. Individual traits such as growth habit, pod and seed size, elongation of the constricted area between pods, nodulation and leaflet size were altered by the presence of GKP 10017 germplasm in many of the hybrid plants. Cercospora arachidicolaHori and Cercosporidium personatum(Berk. & Curt.) Deighton resistances were evaluated for all plants. Several hybrids had few lesions due to either leafspot pathogen. In addition, 24 largeseeded interspecific hybrid selections were compared to the cultivated variety NC 5 for yield. Five selections were superior to both parents at p=0.01. Morphology, disease resistance and yields appeared to be greatly influenced by the wild species GKP 10017 germplasm in plants of the interspecific hybrid population. The potentials of using wild species for improvement of the cultivated peanut are discussed.
Crytology and Morphology of a Tetraploid Sorghum Population Recovered from a Saccharum ✕ Sorghum Hybrid 1
Sugarcane (Saccharum sp.) with 2n = ca. 112 chromosomes was crossed with diploid (2n = 20) sorghum (Sorghum bicolor (L.) Moench), and their hybrids were backcrossed twice with diploid and twice with tetraploid (2n = 40) sorghum. The BC2 individuals, so obtained, were selfed twice to produce a recovered tetraploid sorghum population (BC4F3). Fifty-one BC4F3 individuals, sugarcane and the sorghum parents, were studied cytologically and morphologically. Irregular cytological behavior of recovered sorghum plants, characterized by an increase in bivalent formation and decrease in tetravalent formation at diakinesis (in comparison to their tetraploid ‘Rio’ sorghum parent) indicated that the sorghum chromosomes may be contaminated with sugarcane genetic material. Morphological data were analyzed by cluster analysis, principal component analysis, univariate analysis of variance, F-test, and t-test to study the variability in the hybrid populations and to test the significance of morphological differences among groups. Modified recovered tetraploid sorghums had various combinations of Saccharum characteristics superimposed on a basic Sorghum morphology. Sixteen of 26 plant characters studied were influenced by sugarcane genetic material to varying degrees and frequencies. The presence of these sugarcane characters in recovered sorghums indicated intergenomic genetic exchange.