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V. A. Khan, C. Stevens and J. E. Brown

Early okra production was evaluated using `Clemson Spineless' transplants grown under clear polyethylene mulch plus VisPore row cover (VCM), black polyethylene mulch plus VisPore row cover (VBM), clear polyethylene mulch (CM), black polyethylene mulch (BM) and bare soil (BS) for two years. Early yield (1st four harvests in early June) was significantly greater for VCM treatment while total marketable yield at the end of 8 wks were significantly greater for VCM, BM, and VBM treatments, respectively in both years. Enterprise budget analysis showed that VCM and BM treatments had the highest net-return to management on a per acre basis.

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V. A. Khan, C. Stevens and J. E. Brown

Early okra production was evaluated using `Clemson Spineless' transplants grown under clear polyethylene mulch plus VisPore row cover (VCM), black polyethylene mulch plus VisPore row cover (VBM), clear polyethylene mulch (CM), black polyethylene mulch (BM) and bare soil (BS) for two years. Early yield (1st four harvests in early June) was significantly greater for VCM treatment while total marketable yield at the end of 8 wks were significantly greater for VCM, BM, and VBM treatments, respectively in both years. Enterprise budget analysis showed that VCM and BM treatments had the highest net-return to management on a per acre basis.

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David N. Kuhn, Giri Narasimhan, Kyoko Nakamura, J. Steven Brown, Raymond J. Schnell and Alan W. Meerow

Identifying genetic markers linked to disease resistance in plants is an important goal in marker-assisted selection. Using a candidate-gene approach, we have previously developed genetic markers in cacao (Theobroma cacao L.) for two families of genes involved in disease resistance: non-TIR-NBS-LRR (Toll/Interleukin-1 Receptor-nucleotide binding site-leucine rich repeat) resistance gene homologues and WRKY transcription factor genes; however, we failed to isolate TIR-NBS-LRR genes. Using a novel algorithm to design degenerate primers, we have now isolated TIR-NBS-LRR loci as determined by DNA sequence comparison. These loci have been developed as genetic markers using capillary array electrophoresis (CAE) and single-strand conformational polymorphism (SSCP) analysis. We have mapped three distinct TIR-NBS-LRR loci in an F2 population of cacao and demonstrated that one is located on linkage group 3 and the other two on linkage group 5.

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C. Stevens, V. A. Khan, J. Y. Lu, M. A. Wilson, Z. Haung and J. E. Brown

In 1988 and 1989 a muscadine vineyard at Tuskegeee, Alabama was treated by post plant soil solarization (PSS) (covering of moist soil around 'Carlos' muscadine plants (Vitis rotundifolia Michx.) with clear polyethylene plastic mulch to achieve high soil temperature for 30 and 75 days, respectively during PSS. Grape plants grown in solarized soils showed increases in growth response such as increased yield. Foliage of grape plants was evaluated for reaction to black rot incited by Guignardia bidwellii. A significant reduction of the foliage disease black rot was observed. The number of lesions per leaf, lesion size and percent leaves with lesions were significantly reduced by as much as 56% up to three years after solarization.

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J.E. Brown, R.P. Yates, W.T. Hogue, C. Stevens and V.A. Khan

Yellow crookneck `Dixie' hybrid summer squash, Cucurbita pepo L. var. melopeop Alef., was evaluated at E.V. Smith Research Center, Shorter, Alabama. Summer squash was grown in single rows spaced 6 feet apart. Plants were seeded 18 inches apart within 20-foot row plots. Treatments were: 1) black plastic mulch (BPM), 2) yellow painted plastic mulch (YPM), 3) white plastic mulch (WPM), 4) bare soil (BS), 5) aluminum painted plastic mulch (APM) and 6) bare soil with Diazinon insecticide (BSI). Aphid traps caught more aphids in BS or BPM plots than those from APM or YPM plots. The onset of mosaic disease incidence of squash infected with the two viruses identified as zucchini yellow mosaic and cucumber mosaic was delayed by as much as three weeks when compared to BSI or BS. Summer squash planted in APM, WPM, YPM and BPM produced 96%, 98%, 75% and 21%, respectively, more total squash yield than that produced on bare soil (control). A higher percentage of green squash (virus infected) was produced from plants grown over BPM (72%), BSI (68%), BS (59%), YPM (57%) or WPM (57%) than from APM (39%)

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Raymond Schnell, J. Steven Brown, Cecile Olano, Alan Meerow, Richard Campbell and David Kuhn

Mangifera indica L. germplasm can be classified by origin with the primary groups being cultivars selected from the centers of diversity for the species, India and Southeast Asia, and those selected in Florida and other tropical and subtropical locations. Accessions have also been classified by horticultural type: cultivars that produce monoembryonic seed vs. cultivars that produce polyembryonic seed. In this study, we used 25 microsatellite loci to estimate genetic diversity among 203 accessions. The 25 microsatellite loci had an average of 6.96 alleles per locus and an average PIC value of 0.552. The total propagation error in the collection, i.e., plants that had been incorrectly labeled or grafted, was estimated to be 6.13%. When compared by origin, the Florida cultivars were more closely related to Indian than to Southeast Asian cultivars. Unbiased gene diversity (Hnb) of 0.600 and 0.582 was found for Indian and Southeast Asian cultivars, respectively, and both were higher than Hnb among Florida cultivars (0.538). When compared by horticultural type, Hnb was higher among the polyembryonic types (0.596) than in the monoembryonic types (0.571). Parentage analysis of the Florida cultivars was accomplished using a multistage process based on introduction dates of cultivars into Florida and selection dates of Florida cultivars. Microsatellite marker evidence suggests that as few as four Indian cultivars, and the land race known as `Turpentine', were involved in the early cultivar selections. Florida may not represent a secondary center of diversity; however, the Florida group is a unique set of cultivars selected under similar conditions offering production stability in a wide range of environments.

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Edwin J. Reidel, Patrick H. Brown, Roger A. Duncan and Steven A. Weinbaum

Almond [Prunus dulcis (Mill.) D.A. Webb] yields have increased substantially since the 1961 publication of the Univ. of California (UC) guidelines for leaf potassium (K). Numerous growers and reputable analytical laboratories are concerned that the recommendations for leaf K are inadequate. A highly productive almond orchard with low leaf K was selected to reassess the leaf K critical value of 1.1% to1.4% and determine the relative sensitivity of various yield determinants to inadequate K availability. Baseline yields for 100 individual trees were measured in 1998 and four rates of potassium sulfate were applied under drip irrigation emitters to establish a range of July leaf K concentrations between 0.5% and 2.1%. No relationship was observed between leaf K and post-treatment yield measurements made in 1999. We also monitored individual limb units on trees from the treatment extremes for effects of low K availability on flower number, percentage fruit set, fruit size, spur mortality, and vegetative growth (potential fruiting sites in subsequent years). Those measurements indicated that although current-year yield determinants (percentage fruit set and fruit size) were not influenced by K deficiency, components of future yield were impacted negatively by low K availability: mortality of existing fruiting spurs was increased by K deficiency and growth of fruiting wood was reduced.

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J.E. Brown, R.P Yates, C. Stevens and V.A. Khan

Effects of planting methods and rowcover on the production of yellow crookneck squash, Cucurbita pepo L. var. melopepo Alef., were evaluated over 2 years at the E.V. Smith Research Center, Shorter, Ala. Summer squash was direct-seeded or transplanted in the field with or without black plastic mulch and grown with or without rowcover. Yield of transplanted squash was significantly increased over the same squash direct-seeded. Neither plastic mulch nor rowcover had an effect on summer squash production. Transplants matured 8 to 10 days earlier than the direct-seeded plants.

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J. Steven Brown, R.J. Schnell, J.C. Motamayor, Uilson Lopes, David N. Kuhn and James W. Borrone

A genetic linkage map was created from 146 cacao trees (Theobroma cacao), using an F2 population produced by selfing an F1 progeny of the cross Sca6 and ICS1. Simple sequence repeat (SSR) markers (170) were used principally for this map, with 12 candidate genes [eight resistance gene homologues (RGH) and four stress related WRKY genes], for a total of 182 markers. Joinmap software was used to create the map, and 10 linkage groups were clearly obtained, corresponding to the 10 known chromosomes of cacao. Our map encompassed 671.9 cM, approximately 100 cM less than most previously reported cacao maps, and 213.5 cM less than the one reported high-density map. Approximately 27% of the markers showed significant segregation distortion, mapping together in six genomic areas, four of which also showed distortion in other cacao maps. Two quantitative trait loci (QTL) for resistance to witches' broom disease were found, one producing a major effect and one a minor effect, both showing important dominance effects. One QTL for trunk diameter was found at a point 10.2 cM away from the stronger resistance gene. One RGH flanked the minor QTL for witches' broom resistance, implying possible association. QTLs mapped in F2 populations produce estimates of additive and dominance effects, not obtainable in F1 crosses. As dominance was clearly shown in the QTL found in this study, this population merits further study for evaluation of dominance effects for other traits. This F2 cacao population constitutes a useful link for genomic studies between cacao and cotton, its only widely grown agronomic relative.

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C. Stevens, V. A. Khan, M.A. Wilson, D. J. Collins, J. E. Brown and J. Y. Lu

Agriplastic black mulch (BM), row cover (spunbonded) plus black mulch (RBM) and solarized soil treatments plus black mulch (SBM). row cover plus black mulch on solarized soil (RSBM) and row cover plus solar&d soil (RSBS) increased Floradade tomato yield from 56 to 285%. number of tomatoes and plant height compared to the non-solarized bare soil (BS). When comparing increased growth response (IGR) of the plants grown in the solarized soil with no row cover agriplastic treatments, there was no significant differences among them. When comparing the IGR parameters of tomato plants grown under SBS, BM, and RBS there were no significant differences among them. Spunbonded row cover treatments increased IGR of tomatoes over all treatments without row cover. A significant increase in plant growth promoting rhizobacteria (PGPR) was observed in the rhizosphere soil of Floradade tomatoes grown in solarized soil alone and in those other agriplastic treatments compared to bare soil. There appear to be no differences in PGPR population among SBS and all agriplastic treatments.