E.M. Miyao

Origin of Race 3 of Fusarium oxysporum f. sp. lycopersici at a Single Site in California

ABSTRACT Thirty-nine isolates of Fusarium oxysporum were collected from tomato plants displaying wilt symptoms in a field in California 2 years after F. oxysporum f. sp. lycopersici race 3 was first observed at that location. These and other isolates of F. oxysporum f. sp. lycopersici were characterized by pathogenicity, race, and vegetative compatibility group (VCG). Of the 39 California isolates, 22 were in VCG 0030, 11 in VCG 0031, and six in the newly described VCG 0035. Among the isolates in VCG 0030, 13 were race 3, and nine were race 2. Of the isolates in VCG 0031, seven were race 2, one was race 1, and three were nonpathogenic to tomato. All six isolates in VCG 0035 were race 2. Restriction fragment length polymorphisms (RFLPs) and sequencing of the intergenic spacer (IGS) region of rDNA identified five IGS RFLP haplotypes, which coincided with VCGs, among 60 isolates of F. oxysporum from tomato. Five race 3 isolates from California were of the same genomic DNA RFLP haplotype as a race 2 isolate from the same location, and all 13 race 3 isolates clustered together into a subgroup in the neighbor joining tree. Collective evidence suggests that race 3 in California originated from the local race 2 population.

Weed Control, Yield, and Quality of Processing Tomato Production under Different Irrigation, Tillage, and Herbicide Systems'

A field experiment was conducted near Davis, CA, during the 2003 and 2004 summer growing seasons to compare weed control, yield, and fruit quality in different irrigation and tillage systems in processing tomato. Trial design was a subplots with the main plots as subsurface drip irrigation or furrow irrigation, subplots were standard tillage or conservation tillage, and sub-subplots were herbicide or no herbicide. The hypothesis was that subsurface drip irrigation could limit surface soil wetting and thus inhibit germination and growth of weeds equal to or better than standard tillage and/or herbicides. In both 2003 and 2004, weed densities in the subsurface drip irrigation treatments were over 98% lower than the levels in furrow irrigation treatments. In addition, weed densities were lower in the subsurface drip–conservation till–no herbicide treatment than in any of the furrow irrigation treatments, including the furrow irrigation–standard tillage–herbicide treatments. The time required for a hand-hoeing crew to remove weeds was 5 to 13 times greater in furrow irrigation treatments compared to subsurface drip irrigation treatments. Weed biomass on beds at tomato harvest was 10 to 14 times greater in the furrow systems as compared to the subsurface drip irrigation systems. These results demonstrate the effectiveness of subsurface drip irrigation in controlling weed germination and growth, compared to tillage or herbicide applications. Tomato yield was higher in the subsurface drip irrigation treatment compared to furrow irrigation in 2004. Herbicide treatment increased yield in 2004, but only in the furrow irrigation treatment in 2003. Fruit brix level was not related to treatment in 2003, but was lower in the subsurface drip irrigation plots in 2004. These results indicate that subsurface drip irrigation can reduce weed competition in conservation tillage systems, without requiring herbicide applications. Nomenclature: Tomato, Lycopersicum esculentum Mill. Additional index words: Arid regions, cropping systems, fertigation, hand weeding.

Benefits of Applications of Chlorothalonil for the Control of Black Mold of Tomato

Chlorothalonil was applied 2, 4, 6, 2 and 4, or 4 and 6 weeks prior to tomato harvest in fields in four counties in California over a 3-year period to assess the economic benefits of chlorothalonil applications, if any, on the reduction of black mold caused by Alternaria alternata. The percentage of visually infected fruit was significantly reduced across all four sites in 2 of the 3 years. At one location, the incidence of black mold was reduced over 50% in all 3 years of the study by a single application of the fungicide. Overall, the mean yield of marketable fruit was 79.8 metric tons per hectare. An average of 5.1% of the fruit harvested in all locations and years had visible symptoms of black mold. Generally, the most effective treatment was a single application of the fungicide 6 weeks before harvest, with no further benefit from a second application of the fungicide. Based on the cost of the fungicide and its application, a single dose of chlorothalonil applied to plots in Solano County, where the highest incidence of disease occurred, would net the grower

Estimating soil potassium availability for processing tomato production

160.47 return per hectare. The application of fungicide resulted in significant economic benefits in tests in two of the counties, where the disease is historically a problem.

Managing Fruit Soluble Solids with Late-season Deficit Irrigation in Drip-irrigated Processing Tomato Production

Alternative techniques to evaluate soil potassium (K) availability for processing tomato production were compared to the standard ammonium acetate extraction procedure. Ammonium acetate exchangeable K (Kex), solution-phase K (Ksol), and K fixation potential (Kfp) were evaluated on soils from 40 California fields in which processing tomatoes were grown in 1996–98, and on soils from six K fertilization trials conducted in 1997–98. Ksol was determined in the supernatant of 1:10 mixtures (w/v) of soil and 0.01 M CaCl2, either extracted after an initial 30-minute shaking, or after 7 days of incubation at 25°C. Kfp was estimated by enriching dry soil with 1.0 cmol K kg−1 as aqueous KNO3, air-drying, then either extracting immediately with 1 M NH4Cl or after a 7-day incubation in 0.01 M CaCl2 solution. In all tomato fields, the determinate cultivars ‘Halley’ or ‘Heinz 8892’ were grown. Crop K status was evaluated at full bloom growth stage by K concentration in whole leaves, and at harvest by K concentration in fruit dry mass, total fruit K content (kg ha−1), and the incidence of yellow shoulder (YS, a fruit color disorder affected by soil K availability). Kex ranged from 0.17 to 1.33 cmol kg−1, leaf K from 18 to 43 g kg−1, and fruit K from 26 to 70 g kg−1. Ksol and Kfp were highly correlated with Kex (r=0.94 and 0.86, respectively). The Ksol and Kfp techniques utilizing K measurement after the initial shaking/extraction step were highly correlated with results from the procedures utilizing a 7-day incubation period (r=0.99 and 0.98 for Ksol and Kfp, respectively). Kex was more highly correlated with plant K status than either Ksol or Kfp, but correlations ranged from only −0.35 (for YS incidence) to 0.57 (for fruit K content). Potassium application reduced YS in 2 of 4 fertilization trials in which the disorder was prevalent, but none of the measures of soil K availability were predictive of either YS incidence, nor of fruit yield response to fertilization.