Pink root (Phomaterrestris) is among the major limiting factors for the production of sweet onions on Maui, Hawaii. Few management options exist for the control of pink root in onions. Two split-plot experiments were conducted in the area of Kula, Maui, over 2 years to evaluate several alternative management practices. In Expt. 1, the main plots were a rotation with cabbage, solarization with a clear plastic mulch, and a fallow period. Subplots were plus or minus Vapam fumigation. Sub-subplots were biomass application of Sudex or rape, inoculation with an EM biostimulant, and control. Each treatment had four replications for a total of 96 plots. In the follow-up experiment, the main plots were Vapam fumigation, rotation with either a Sudex or rape cover crop, and controls. The subplots were plus or minus EM biostimulant application. In Expt. 1, three separate treatments: solarization, cabbage rotation, and Sudex incorporation had a synergistic effect with Vapam fumigation. Fumigation and solarization also decreased pink root incidence. Rape contributed to a decreased disease incidence while EM contributed to increased bulb size. In Expt. 2, EM and rape contributed to increased yields. Rape and sorghum rotations contributed to decreased pink root incidence. EM inoculation had differential effects on several diseases, contributing to reduced bacterial bulb rot levels. The data indicate that growers may have several alternative management tools at their disposal, in addition to proper varietal selection, to improve yields and reduce disease incidence in sweet onions.
Hector Valenzuela, Robin Shimabuku, and John Cho
Mikel R. Stevens, John W. Scott, John J. Cho, Bradley D. Geary, and Frederic D. Memmott
Tomato spotted wilt virus (TSWV), a tospovirus, is a thrips-vectored disease infecting more than 1000 species of both monocots and dicots, including many species of agriculture importance. TSWV is the limiting factor for tomato (Lycopersicum esculentum Mill.) production in several areas of the world. For a number of years, the Sw-5 gene (derived from L. peruvianum Mill.) has provided acceptable control of this disease. Recently, Sw-5 derived resistance has been overcome by virulent pathogen isolate(s) in tomato production areas such as Spain and Italy. In earlier studies, we identified a potential new source of resistance to TSWV derived from L. chilense Dun. accession LA 1938. In a set of recent field studies, it was demonstrated that this putative new source of resistance was highly resistant to TSWV in Hawaii, Florida/Georgia, and South Africa. Furthermore, greenhouse screening trials have clearly demonstrated that the L. chilense source of TSWV resistance is resistant to isolates that overcome tomatoes homozygous for Sw-5. In these same greenhouse and field studies, there is uniform evidence that this resistance is dominant. Subsequent greenhouse studies suggest that this resistance is controlled by a single gene. Studies have been initiated to verify the inheritance of the gene(s) and to develop linked molecular markers. Furthermore, studies are under way in Australia to test this resistance on non-TSWV tospoviruses. If the data demonstrate that this is a single dominant gene we suggest this gene be designated Sw-7.
Alyssa H. Cho, Carlene A. Chase, Danielle D. Treadwell, Rosalie L. Koenig, John Bradley Morris, and Jose Pablo Morales-Payan
A field study was conducted in 2008 and 2009 in Citra, FL, to evaluate the effects of seeding rate and removal of apical dominance of sunn hemp (Crotalaria juncea L.) on weed suppression and seed production by sunn hemp. Three seeding rates of sunn hemp were used: a representative seed production rate of 11 kg·ha−1, an intermediate seeding rate of 28 kg·ha−1, and a cover crop seeding rate of 45 kg·ha−1. Cutting the main stem at 3, 4, or 5 weeks after planting to break apical dominance was compared with an uncut treatment. Cutting had no significant effect on shoot biomass, photosynthetically active radiation (PAR) penetrating the canopy, and nondestructive leaf area index (LAI). As a result, cutting also had no effect on weed density and biomass in 2008 and very little effect in 2009. Increase in seeding rate resulted in linear decrease in PAR and increase in LAI in both years. Seeding rate had a greater effect on suppression of weed biomass than on suppression of weed density. There was a linear decline in sunn hemp branching with increased seeding rate in 2009 and, averaged across years, flower number decreased linearly with increased seeding rate. Cutting to break apical dominance induced branching but had no effect on flower number. No seed pod production occurred and we postulate that the lack of seed production may be the result of the absence of effective pollinators in fall when short-day varieties of sunn hemp flower in Florida.