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M.B. Fiely and T.E. Morelock

Spinach (Spinacia oleracea L.) varies in tolerance to saturated soil conditions. Plant vigor was assessed for plants flooded in autoclaved and nonautoclaved field soil. Decline of vigor was more rapid for plants flooded in nonautoclaved field soil, indicating that flooding tolerance may be influenced by soil borne pathogens.

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C.H. Becker and T.E. Morelock

Southernpea (Vigna unguiculata) is a popular home garden, fresh-market, and processing vegetable in the southeastern United States. Processing schedules are normally controlled by planting the same variety at different dates. Difference in genetic maturity would allow growers to stagger harvest dates by planting different maturity peas on the same day and allow genotype to alter harvest dates. This procedure would allow growers to better utilize available soil moisture and optimum planting dates. Ten southernpea varieties and breeding lines representing early, medium, and late maturity were planted in Kibler, Ark., during the summers of 1994 and 1995. Five different planting dates were used. Flowering dates and days to maturity were recorded and plots were harvested for yield. Results indicate that relative days to maturity can be significantly shortened or lengthened by the time of planting. Varieties planted in early June or early August took longer to mature then when they were planted in late June or early July.

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M.B. Fiely and T.E. Morelock

Spinach (Spinacia oleracea L.) varies in tolerance to saturated soil conditions. Plant vigor was assessed for plants flooded in autoclaved and nonautoclaved field soil. Decline of vigor was more rapid for plants flooded in nonautoclaved field soil, indicating that flooding tolerance may be influenced by soil borne pathogens.

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T.E. Morelock, P.W. Simon, and C.E. Peterson

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L.P. Brandenberger, T.E. Morelock, and J.C. Correll

Field observations indicate that polygenic resistance to downy mildew (Peronospora farinosa f. sp. spinaciae) was observed during the course of a breeding program to develop polygenic resistance to white rust (Albugo occidentalis). Field studies were initiated using five cultivars and one breeding line to quantify the level of resistance to downy mildew and white rust. Separate plots were inoculated with each pathogen at a specific spore concentration and then subjected to a minimum dew period of 12h. Infection was quantified by measuring latent period, lesion number, lesion size, sporulation and percent leaf area infected.

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T.E. Morelock, D.R. Motes, and A.R. Gonzalez

Southernpea (Vigna unguiculata) is an important crop in the southern United States. The Arkansas Agricultural Experiment Station announces the release of three varieties. `Excel' produces a compact bush plant, from 45–60 cm tall with no basal runners. Pods are deep purple, 20–25 cm long and shell easily at the green mature stage. Flowering and fruiting are concentrated, with the pods produced at the top of the plant on medium-length peduncles. Seed has a bright pinkeye and is similar in size to pinkeye purple hull BVR but matures 3–4 days earlier. `Early Scarlet' produces a medium sized plant, from 60–75 cm tall with no basal runners. Pods are light red, 20–25 cm long and shell easily at the green mature stage. Flowering and fruiting are concentrated at the top of the plant with pods produced on medium-length peduncles. Seed has a light pinkeye and is similar in size to `Pinkeye Purple Hull BVR' but matures 2–3 days earlier. `Arkansas Blackeye #1' produces a bush plant, from 50–65 cm tall with no basal runners. The pods are silver, 20–25 cm long and shell easily. Flowering and fruiting are concentrated with the pods produced in the top of the plant on medium-length peduncles. Seed has a distinct medium-sized blackeye and the seed are very similar in size, type and eye pattern to `California #5 Blackeye'. Maturity is normally 2–3 days earlier than `Pinkeye Purple Hull BVR'.

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L.A. Wasilwa, T.E. Morelock, and J.C. Correll

Anthracnose is a destructive foliage and fruit disease of cucurbits worldwide, particularly on cucumber, watermelon, and cantaloupe. Three fungal taxa have been implicated in the cucurbit anthracnose complex [Colletotrichum orbiculare (CO), C. magna (CM), and the putative teleomorph Glomerella cingulata var. orbiculare (GC)]. In the past 7 years we have assembled a large geographically diverse collection of cucurbit isolates that have been characterized for virulence, vegetative (heterokaryon) compatibility, and mitochondrial and nuclear DNA RFLPs. All isolates that are pathogenic on cucurbit foliage are CO, belong to one of the four VCGs, and belong to a single mtDNA RFLP haplotype. Three races of CO (1, 2, and 2B) can be distinguished by their disease reactions on cucumber (`Marketer' and `H19') and watermelon (`Black Diamond' and `Charleston Gray') differentials. Race 1 (cucumber pathogen) and race 2 (watermelon pathogen) were the most common. Examination of virulence on cucurbit fruit indicates that CM and GC are more aggressive than CO, indicating that they could primarily be fruit-rot pathogens. Race 1 and 2 have been used effectively for screening disease resistance in cucumber and watermelon. Isolates of CM, GC, and Colletotrichum spp. recovered from fruit lesions were not pathogenic or were weakly virulent on cucurbit foliage and were diverse with regard to VCGs, nuDNA, and mtDNA RFLPs. However, CM and GC were more virulent on cucurbit fruit than CO.

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J. M. Al-Khayri, F. H. Huang, and T. E. Morelock

Regenerated spinach (Spinacia oleracea L.) maintained under a 10-h photoperiod (65 uE m-2 s-1) after an incubation period on a GA-containing medium were induced to flower in vitro. The plantlets were regenerated from callus initiated on MS medium with 2.0 mg L-1 kinetin and 0.5 mg L-1 2,4-D and were subsequently transferred to a medium containing 2.0 mg L-1 kinetin, 1.0 mg L-1 GA, and 0.01 mg L-1 2-4,D. While on the regeneration medium, the cultures were exposed to a long-day photoperiod. Regenerants were transferred to an IBA-containing medium for rooting, after which flowering was observed. In vitro flowering plantlets exhibited male and female flowers depending on the sex of the explant donor. Female plantlets developed seeds in the culture vessels. This method of seed production from regenerants can eliminate time-consuming steps in acclimation, transplanting to soil, and plant maintenance.

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L.A. Wasilwa, T.E. Morelock, and J.C. Correll

Anthracnose of cucurbits, caused by Colletotrichum orbiculare, is composed of three races (race 1, 2, and 2B). The inheritance of race 1 in cucumber is reported to be controlled by a single recessive gene. Although the mode of inheritance to race 2 in cucumber has not been determined, it has been suggested that is quantitatively inherited. Four cucumber cultivars, H19 from two sources [the commercial seed (P1) and the breeders seed (P2)], Pixie (P3), and Marketer (P4), that were considered highly resistant, moderately resistant and highly susceptible, respectively, to race 2 were used as the parents in this study. Crosses between resistant × susceptible and resistant × moderately resistant were made. Some reciprocal crosses also were made. The F1 progeny were then evaluated for resistance to race 2 in a cotyledon assay. Disease severity was assessed 8 days after inoculation using a disease rating scale of 0–7, whereby 0 = healthy plant and 7 = 100% chlorosis or necrosis. All progeny from P1 × P1 were highly resistant (disease severity 19 < 2.5); P2 × P2 and P3 × P3 were highly moderately resistant (disease severity 2.6–4.9); and all P4 × P4 progeny were highly susceptible (disease severity > 5.0) to race 2. All F1 progeny showed a continuum of disease ratings from highly resistant to moderately resistant to race 2. The disease ratings of the F1 progeny would indicate that resistance to race 2 is controlled by multiple genes.

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L.P. Brandenberger, T.E. Morelock, and J.C. Correll

Field observations indicate that polygenic resistance to downy mildew (Peronospora farinosa f. sp. spinaciae) was observed during the course of a breeding program to develop polygenic resistance to white rust (Albugo occidentalis). Field studies were initiated using five cultivars and one breeding line to quantify the level of resistance to downy mildew and white rust. Separate plots were inoculated with each pathogen at a specific spore concentration and then subjected to a minimum dew period of 12h. Infection was quantified by measuring latent period, lesion number, lesion size, sporulation and percent leaf area infected.