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- Author or Editor: Bruce Reisch x
- HortScience x
Abstract
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.
A project to develop a linkage map of the Vitis genome is underway using an interspecific hybrid grape population from `Cayuga White' × `Aurore'. The linkage map is based on 15 isozyme, 13 RFLP and more than 350 RAPD markers. This information is being combined with segregation data for viticulturally important traits including disease resistance to identify QTLs and mark simply inherited traits. Molecular markers, when linked with morphological traits, will find great application in map-based cloning and marker-assisted selection in grape breeding. We have also analyzed genome size of three genera of Vitacae (Ampelopsis, Parthenocissus and Vitis) and 15 Vitis species as well as 15 diploid cultivars using flow cytometry. DNA content varied from 0.84 to 1.40 pg/2C. The relative small genome size indicates that Vitis is a good candidate for molecular genome analysis. All this information will help us understand Vitis genome organization and reliability of identifying a gene linked to a marker in different populations.
Abstract
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.
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.