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- Author or Editor: C.W. Kuhn x
A mutant trait discovered in a planting of ‘Knuckle Purple Hull’ cowpea [Vigna unguiculata (L.) Walk.] is characterized by proliferated leaf buds, by narrow, elongated, distorted leaflets with irregular margins and abnormal vein curvature, and by sterility caused by failure of the style to elongate. In most flowers, the stigma remained enclosed by the united stamens. Inheritance of this trait is governed by a single recessive gene for which the symbol pbs, for proliferated buds, is proposed.
Southern pea (cowpea) plants reacted with 4 types of response to southern bean mosaic virus-cowpea strain: 1) susceptible, 2) hypersensitive, 3) hypersensitive plus systemic necrosis, and 4) symptomless reaction. The hypersensitive reaction (resistant) on inoculated leaves was dominant and inheritance was controlled by a single gene pair. In segregating populations of some crosses, systemic necrosis followed the initial hypersensitivity. Although the inheritance of the systemic necrosis was not determined, it appeared to be influenced by temperature. Plants without systemic necrosis were selected from F3 populations.
The College of Agriculture of the Univ. of Georgia releases 3 cowpea (Vigna unguiculata (L.) Walp.) cultivars which are resistant to blackeye cowpea mosaic virus (B1CMV): ‘Pinkeye Purple Hull-BVR’, ‘White Acre-BVR’, and ‘Corona’. B1CMV causes the most important disease of cowpea in Georgia (3), and it has been found in Alabama (3), South Carolina (3), and Texas (G.L. Philley, personal communication). Infection of cowpea with B1CMV causes significant losses. More important, however, is the synergistic disease reaction (cowpea stunt) which occurs with mixed infections of B1CMV and cucumber mosaic virus (CMV) (4). These 3 cultivars should be useful for commercial production and home gardens, and as parents for breeding programs.
Mango (Mangifera indica L.) germplasm can be classified by origin with the primary groups being cultivars selected from the centers of diversity for the species, India and Southeast Asia, and those selected in Florida and other tropical and subtropical locations. Accessions have also been classified by horticultural type: cultivars that produce monoembryonic seed vs. cultivars that produce polyembryonic seed. In this study we used 25 microsatellite loci to estimate genetic diversity among 203 unique mangos (M. indica), two M. griffithii Hook. f., and three M. odorata Griff. accessions maintained at the National Germplasm Repository and by Fairchild Tropical Botanic Garden in Miami, Fla. The 25 microsatellite loci had an average of 6.96 alleles per locus and an average polymorphism information content (PIC) value of 0.552 for the M. indica population. The total propagation error in the collection (i.e., plants that had been incorrectly labeled or grafted) was estimated to be 6.13%. When compared by origin, the Florida cultivars were more closely related to Indian than to Southeast Asian cultivars. Unbiased gene diversity (Hnb) of 0.600 and 0.582 was found for Indian and Southeast Asian cultivars, respectively, and both were higher than Hnb among Florida cultivars (0.538). When compared by horticultural type, Hnb was higher among the polyembryonic types (0.596) than in the monoembryonic types (0.571). Parentage analysis of the Florida cultivars was accomplished using a multistage process based on introduction dates of cultivars into Florida and selection dates of Florida cultivars. In total, 64 Florida cultivars were evaluated over four generations. Microsatellite marker evidence suggests that as few as four Indian cultivars, and the land race known as `Turpentine', were involved in the early cultivar selections. Florida may not represent a secondary center of diversity; however, the Florida group is a unique set of cultivars selected under similar conditions offering production stability in a wide range of environments.
A genetic linkage map was created from 146 cacao trees (Theobroma cacao), using an F2 population produced by selfing an F1 progeny of the cross Sca6 and ICS1. Simple sequence repeat (SSR) markers (170) were used principally for this map, with 12 candidate genes [eight resistance gene homologues (RGH) and four stress related WRKY genes], for a total of 182 markers. Joinmap software was used to create the map, and 10 linkage groups were clearly obtained, corresponding to the 10 known chromosomes of cacao. Our map encompassed 671.9 cM, approximately 100 cM less than most previously reported cacao maps, and 213.5 cM less than the one reported high-density map. Approximately 27% of the markers showed significant segregation distortion, mapping together in six genomic areas, four of which also showed distortion in other cacao maps. Two quantitative trait loci (QTL) for resistance to witches' broom disease were found, one producing a major effect and one a minor effect, both showing important dominance effects. One QTL for trunk diameter was found at a point 10.2 cM away from the stronger resistance gene. One RGH flanked the minor QTL for witches' broom resistance, implying possible association. QTLs mapped in F2 populations produce estimates of additive and dominance effects, not obtainable in F1 crosses. As dominance was clearly shown in the QTL found in this study, this population merits further study for evaluation of dominance effects for other traits. This F2 cacao population constitutes a useful link for genomic studies between cacao and cotton, its only widely grown agronomic relative.