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  • Author or Editor: G.E. Boyhan x
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Certified organic production is challenging in the southeastern United States due to high weed, insect, and disease pressure. Maintaining and building soil organic carbon in midscale organic production systems can also be difficult due to the warm, moist conditions that promote decomposition. Focusing on cool-season cash crops paired with warm-season cover crops may help alleviate these production problems. This 3-year study (2011–13) evaluated two vegetable rotations of cool-season crops with cover crops for their productivity, disease management, and soil building potential in Watkinsville, GA. In the first rotation, cool-season cash crops included onion (Allium cepa), strawberry (Fragaria ×ananassa), and potato (Solanum tuberosum). These crops were rotated with green bean (Phaseolus vulgaris), oats/austrian winter pea (Avena sativa/Pisum sativum ssp. arvense), southernpea (Vigna unguiculata), and sunn hemp (Crotalaria juncea). In the second rotation, cool-season cash crops included onion, broccoli (Brassica oleracea Italica group), lettuce (Lactuca sativa), and carrot (Daucus carota ssp. sativus). These were rotated with millet (Urochloa ramosa), sunn hemp, egyptian wheat/iron clay pea (Sorghum sp./Vigna unguiculata), and sorghum × sudangrass (Sorghum bicolor × S. bicolor var. sudanese)/iron clay pea. Onion yields in both rotations were at least 80% of average yields in Georgia. Lettuce yields were at least double the average yields in Georgia and were comparable to national averages in the 2nd and 3rd years of the study. Strawberry yields in these rotations were lower than Georgia averages in all 3 years with a trend of lower yields over the course of the study. By contrast, potato, although lower than average yields in Georgia increased each year of the study. Broccoli yields in the first year were substantially lower than average Georgia yields, but were comparable to average yields in the 2nd year. Carrot remained less than half of average Georgia yields. Green bean were half of average Georgia yields in the 2nd year and were comparable to average yields in the 3rd year. As expected from what is observed in cool-season organic vegetable production in Georgia, disease pressure was low. Cover crops maintained soil organic carbon (C) with a small increase in active C; however, there was a net loss of potentially mineralizable nitrogen (PMN). Active C averaged across both rotations at the beginning of the study at 464 mg·kg−1 and averaged 572 mg·kg−1 at the end of the study. On the basis of this study, using cover crops can maintain soil carbon without the addition of carbon sources such as compost. Finally, longer term work needs to be done to assess soil management strategies.

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Graft incompatibility of 3 chestnut Castanea spp. was studied. Nine American chestnut C. crenata Sieb. & Zucc and 15 Chinese chestnut C. mollissima Bl. cultivars used as scions were tested on rootstocks of Chinese chestnut. Interspecific grafts with 7 of 9 American chestnut selections had satisfactory graft compatibility on Chinese chestnut rootstocks (70%-100%), so did 6 of 8 Japanese chestnuts. Twelve and 10 out of 15 Chinese cultivars had high graft compatibility on Chinese chestnut rootstocks. Three Chinese cultivars with less than 50% success were probably due to very diverse genetic variation within one cultivar group of Chinese chestnuts. Spring grafts always had higher percent success rates than fall grafts. Graft incompatibility was not found to be related to the cambial isoperoxidase banding patterns in the present study.

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Six lines of watermelon or related germplasm were evaluated for resistance to the Egyptian strain of zucchini yellow mosaic virus (ZYMV-E). `Egun' had the highest level of resistance of the lines tested based on enzyme-linked immunosorbent assays and visual ratings. PIs 386025, 386026, and 494528 appear to have intermediate resistance.

PIs 386025 and 386026, both resistant to the Florida strain of ZYMV, were analyzed in crosses with 'AU-Producer'. No Mendelian ratios were evident, therefore generation mean analysis was used to evaluate this material.

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In a screening test of 76 PIs, commercial Chinese watermelons, and `Crimson Sweet', PI512385 had the highest disease resistance with a mean rating of 4.5 on a 1-9 scale with 1 = resistant and 9 = susceptible. A second test with PI512385 included material with previously reported resistance (PIs 270550, 326515, 271775, 271779, 203551, 299379 and 189225) and `Crimson Sweet', a susceptible check showed PI512385 had significantly more resistance than `Crimson Sweet' but was not significantly more resistant than the PIs. PI512385 had a mean rating of 2.2 in the second test.

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