Botrytis cinerea, the causal agent of Botrytis bunch rot and gray mold, is the number one postharvest disease of fresh grapes in the United States. Fungicide applications are used to manage the disease, but fungicide-resistant isolates are common and postharvest losses occur annually. Host resistance is needed for long-term management of the disease. Sources of resistance in grape have been identified, but often have poor fruit quality. In this study, 27 grape lines (cultigens and species), including high fruit–quality Vitis vinifera, were evaluated for fruit and leaf susceptibility to two isolates of B. cinerea. No significant differences in virulence or pathogenicity were detected between the two isolates, but differences in disease incidence were evident among lines in leaves and berries. Most V. vinifera cultivars evaluated had high disease incidence in berries, whereas complex hybrids, Vitis aestivalus and Vitis arizonica, had low- to moderate disease incidence. Two V. vinifera breeding lines had moderate susceptibility (<50% disease) to Botrytis bunch rot when inoculated with either isolate. Only one V. vinifera line had little (<5%) to no berry or leaf disease when inoculated with either isolate. Moderate resistance (10% to 25%) was detected in Vitis spp., and a single V. vinifera line. Correlations were examined among soluble solids, leaf susceptibility, and fruit susceptibility. No correlations between soluble solids and disease susceptibility (leaves or berries) were identified, but moderate correlations between leaf and berry susceptibility were observed. Moderate resistance to Botrytis bunch rot and leaf spot were detected in Vitis breeding lines, suggesting these may be useful for developing grape cultivars with high fruit quality and resistance to B. cinerea.
Charles S. Krasnow, Rachel P. Naegele and Mary K. Hausbeck
Phytophthora blight is a destructive disease of cucurbits affecting the fruit, leaves, crown, and/or roots. Ten cucurbit PIs with known partial resistance to Phytophthora capsici root and crown rot were evaluated for resistance to Phytophthora fruit rot. Unwounded fruit from field-grown plants of Cucurbita moschata and C. pepo were inoculated in a controlled environment at 7 to 10 or 21 to 24 days post-pollination (dpp) with virulent P. capsici isolates to examine the effect of fruit age on disease development. Inoculated fruit were rated for lesion area and pathogen mycelial growth 7 days post-inoculation (dpi); fruit length, diameter, and pericarp thickness were also rated. Two C. pepo accessions (PI 169417 and PI 181761) had significant resistance to Phytophthora fruit rot at both 7 to 10 dpp and 21 to 24 dpp. All accessions evaluated displayed reduced disease susceptibility as the fruit aged.
Todd C. Wehner, Rachel P. Naegele and Penelope Perkins-Veazie
Citrulline, arginine, and lycopene are naturally occurring compounds found in watermelon, Citrullus lanatus (Thumb) Matsum & Nakai, with beneficial effects on plant growth and human health. This study evaluated seven commercial cultivars and one breeding line for citrulline, arginine, and lycopene content in mature fruit grown at two locations in North Carolina. Correlations among these compounds and fruit quality traits (percent soluble solids and flesh pH) were evaluated. Watermelon cultigens evaluated were chosen for their fruit trait diversity. ‘Yellow Doll’ and NC-517 possessed the highest citrulline and combined concentration of citrulline and arginine of all cultigens evaluated. Lycopene content was highest in ‘Dixielee’, followed by ‘Sugar Baby’, and ‘Allsweet’, each of which have different shades of red flesh color. Location and its interaction with genotype had no significant effect on arginine or lycopene concentration. Broad-sense heritability was estimated for each trait. Arginine content (89%) and lycopene content (99%) had very high heritability. Citrulline content (41%), percent soluble solids (46%), and flesh pH (61%) had moderate heritability. Lycopene was positively correlated with flesh pH (r = 0.517) and negatively correlated with percent soluble solids (r = −0.344). Arginine content had a weak negative correlation with flesh pH (r = −0.343) and was not correlated with percent soluble solids.
Melisa Crane, Todd C. Wehner and Rachel P. Naegele
Cucumber (Cucumis sativus L.) is one of the most popular vegetable crops grown in U.S. home and urban gardens. The objectives of this study were to identify cultivars and planting densities for high yield of container-grown cucumbers. Additional objectives were to determine the value of field trials for predicting cucumber performance in containers and to evaluate different plant types (dwarf-determinate vs. tall-indeterminate, gynoecious vs. monoecious, pickling vs. slicing) for container use and disease severity across cultivars. Fourteen cultivars and breeding lines were tested at three planting densities in two seasons for yield, quality, and disease resistance in field and patio trials. Significant differences were detected for seasons, cultivars, and densities. Yields were highest in the spring season compared with the summer season, and the best performance was obtained using three plants per 12 L container. There was a high correlation between patio and field trials, allowing extension specialists to recommend cucumber cultivars with high yield, high quality, and disease resistance based on field trial data. Home gardeners who want space-saving, high-yielding cucumbers with tender skin should consider a dwarf-determinate, pickling type that is monoecious. With monoecious type, no pollenizer is needed, and the harvest will be spread over more weeks than would be for gynoecious types.