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- Author or Editor: Bruce Reisch x
Various procedures were compared to identify a technique that would produce clear countable chromosomes in grape (Vitis L.) root tip squashes. Harvesting roots at 1100 hr from greenhouse-grown plants, pretreating with 0.02 m 8-hydroxyquinoline at 18°C for 6 hr, fixing in Farmer's Fluid at 26° for 24 hr, hydrolyzing in 1 n HCl at 60° for 1 hr, and staining with an altered form of carbol fuchsin gave the best results.
Pollen from 157 genotypes of grape (Vitis sp.) were scanned for the occurrence of grains ≥30 μm in diameter. Eighteen diploid genotypes produced from 3% to 36% large pollen grains. Four of these produced distinctly oval-shaped grains. Eleven tetraploid genotypes produced from 47% to 87% large pollen. Large grains in diploid genotypes may be unreduced gametes that could be used in interploid crossing to breed hybrid tetraploids.
Genetic analysis of 11 allozyme polymorphisms was performed on the progeny of ‘Cayuga White’ × ‘Aurora’, two complex interspecific grape (Vitis) hybrids. Segregation for most of the polymorphisms closely approximated monogenic Mendelian ratios, and eight new isozyme loci were defined for grape. Joint segregation analysis among the isozyme loci revealed three multilocus linkage groups. These results demonstrate that sufficient allozyme polymorphism exists in grape to establish many multilocus linkage groups and that this genetic analysis can be accomplished using extant progeny or progeny readily produced from highly heterozygous clones.
Grapevine downy mildew (DM), caused by the oomycete Plasmopara viticola (Berk. & Curt.) Berlese & de Toni, is a major disease, especially in humid viticultural areas. Development of resistant cultivars is an important objective for grapevine breeding. To establish a reliable and inexpensive quantitative method to aid in breeding for DM resistance, we improved the method for counting the number of sporangia on leaf discs, and developed a method for counting the number of sporangia in solution. To prevent the loss of DM sporangia from adhesion onto plastic ware, we found as little as 0.01% Tween 20 was effective. On the other hand, this detergent was shown to have a severe inhibitory effect upon DM infection of leaves. We developed a sporangia counting method using dried droplets of DM suspensions, and the method was highly correlated with counting by hemacytometer (R 2 > 0.96). The nonparametric Spearman’s rank correlations between visual rating and the number of the sporangia were as high as ρ = 0.82 to 0.91, suggesting that evaluation by the visual rating could provide a good estimate of the sporangia numbers on leaf discs. We established a high-throughput and inexpensive method with acceptable accuracy for DM resistance evaluation based on a leaf disc assay, and our results suggested that visual ratings of infected leaf discs provide a good estimate of sporangia numbers.
Variegation in Vitis hybrids was investigated to confirm the inheritance as a single, recessive gene as previously proposed and commonly observed in breeding programs. Variegated leaves have ornamental appeal, but the phenotype is sublethal in some environments. Twenty-nine grape families were characterized for variegation including F1, S1, and S2 populations. The majority segregated 3 wild type (WT):1 variegated and were supported by chi-square tests. Four populations had segregation ratios supporting 15:1 or 1:1 models, and a unique flecking phenotype was identified in a Landot 4511 S1 population that suggested the interaction of two recessive loci. A variegated parent was selfed to produce progeny with no WT offspring and was segregated 0:1. Marker trait associations including bulk segregant analysis (BSA), genome-wide association mapping, and quantitative trait loci (QTL) mapping was used on three populations. On chromosome 14, Lvar1 was identified and mapped to 24.5 to 29.5 Mb and associated closely with rhAmpSeq marker 14_27607541. Lvar2 was associated with rhAmpSeq marker 11_18433819 on chromosome 11 at 12.2 to 18.4 Mb. The identification of two loci and the segregation data in some populations suggest that grape breeding germplasm segregates for two recessive loci. The pedigree records suggest that ‘Frontenac’ inherited one of these loci, and that Landot 4511, an ancestor of many populations tested in this experiment, may carry two loci. A total of 252 candidate genes were identified at these loci, including a key target—adenosine triphosphate (ATP)-dependent zinc metalloprotease FtsH6, involved in photosystem II and similar to the var2 mutant in Arabidopsis. This knowledge can help breeders select for ornamental grapevines or eliminate variegation from their breeding programs.