Graft compatibility was investigated for 15 Chinese chestnut (Castanea mollissima Bl.) cultivars, nine American chestnut [C. dentata (Marsh.) Borkh.] selections, six Japanese chestnut (C. crenata Sieb.) cultivars, and two putative Japanese hybrids on two known rootstocks of Chinese chestnut. Intraspecific grafting of Chinese chestnut resulted in 80% success after two growing seasons. An unusual anatomical structure of the chestnut stem had a significant effect on graft success. The phloem fiber bundles related to graft failure are described in the study. Interspecific grafts of seven American and five Japanese chestnut selections resulted in ≥70% success. The putative Japanese hybrids had a significantly lower success rate (<50%) regardless of rootstocks. A marked graft incompatibility was found in one Japanese/Chinese and two American/Chinese combinations. Graft incompatibility related to morphological abnormalities at the graft union was also observed in interspecific grafts. Comparisons of cambial isoperoxidase isozymes between successful and unsuccessful grafts did not support the hypothesis that peroxidase isozymes are indicators of rootstock-scion compatibility. The results suggest that genetic incompatibility is not a major cause of graft failure in Chinese chestnut.

Allozyme genetic variability in three chestnut (Castanea) species was investigated using 19 loci from ten enzyme systems. G-tests of heterogeneity of isozymic allele distribution showed significant differences between the three species at 15 of the 19 loci, and between the 13 C. mollissima populations at 13 of the 19 loci examined. C. mollissima was found to possess a significantly-higher value of mean gene heterozygosity (H=0.3050±0.0419), the percentage of polymorphic loci (P=84.21%) and the average number of alleles per locus (A=2.05), than any other species in the Castanea section Eucastanon. When the genetic variability of populations of C. mollissima from four regions in China was investigated, the population from the Changjiang river region showed a markedly higher mean gene heterozygosity (H=0.3480±0.0436) than populations from the other regions. Genetic relationships among the four regions were assessed by Nei's genetic identity I and standard genetic distance D. An approximately-identical distance between the population from the Changjiang river region and populations from the three other regions was observed, while populations from the latter regions showed almost the same genetic distance from each other. These data, when considered with information existing prior to this study, contribute to an understanding of the possible origin and progenitor of the chestnut species.

Abstract:The physical, chemical and sensory characteristics of 15 plum cultivars and selections grown at Byron, GA and Clanton, AL in 1989 and 1990 were investigated. Selection BY68-1262 produced significantly larger fruit than the other plum cultivars and selections evaluated followed by ' AU-Rubrum ' and 'Rubysweet'. 'Methley' fruit was the smallest. Hue angle (8) values ranged from 105" for 'Byrongold', a yellow-skin cultivar, to 6" for BY68-1262, a deep-purple skin selection. Average firmness of the maturity 2 plums was 25 N. Mean chemical compositions for all cultivars were as follows: soluble solids-127g kg-' ; acidity-1744 g kg-'; soluble solids to acidity ratio-7.4, and total sugar content-96 g kg-I. Hedonic scores and 'just right' percentages showed that panelists preferred ' Rubysweet' and 'Segundo' plums harvested in 1989 and BY74074, ' AU-Amber' and BY68-98 plums harvested in 1990. ' AU-Producer' had the lowest hedonic score. 'Robusto' and 'AU-Rosa' had the highest mean peel bitterness rating.

var has good resistance to race 2 anthracnose, fusarium wilt, and gummy stem blight. 'AU-Sweet Scarlet' originated from the crosses 'Crimson Sweet' x PI 189225, 'All Sweet' x PI 362515, and 'Calhoun Sweet' x 'W.R. Peacock' (Fig. 1). Resistance to gummy stem blight and race 2 anthracnose was incorporated into the breeding lines from plant introductions by a backcross program. Progeny were selected in a screening program with inoculation tests in an incubation chamber and greenhouse as previously described (Norton, 1979; Sowell, 1975; Sowell and Pointer, 1962; Sowell et al., 1980; Suvanprakorn and Norton, 1980). Reaction to fusarium wilt was recorded on plants grown in pots in a greenhouse (Hopkins et al., 1987). The resistance was also observed in field plots heavily infected with fusarium, as indicated by plant injury the previous season. Selections were made annually for disease-resistant seedlings and high yield of excellent-quality fruit. Resistance to gummy stem blight and race 2 anthracnose was obtained from PI 189225 and PI 362515. Resistance to fusarium wilt was obtained from 'Crimson Sweet', 'Allsweet', 'Calhoun Gray', 'W.R. Peacock', and the plant introductions. Multiple-disease resistance of 'AU-Sweet Scarlet' has been good in field plantings (Table 1). 'AU-Sweet Scarlet' has been grown as AW-82-50CS in trials at the E.V. Smith Research Center and at several substations of the Alabama Agricultural Experiment Station, Auburn Univ.; in the Southern Cooperative Watermelon Trials in other southern states;

Of 153 plant introductions (PI), breeding lines, and commercial cultivars tested by mechanical inoculations in the greenhouse, only PI 482261-1, `Egun', PI 494528, PI 386026, and PI 386025 showed any resistance to the Florida strain of zucchini yellow mosaic virus. PI 482261-1 and `Egun' are Citrullus lanatus, the others are citron types, Citrullus colocynthis. This is the first report of resistance in PI 386026, PI 386025, and the cultivar `Egun'.