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A selection of Congo produced fruit that were not infected by blotch (pathogen Acidovorax avenae subsp. citrulli) in a replicated trial interplanted with infected seedlings. Ninety percent of Congo fruit not infected with the bacterial pathogen had a darker green background than those infected. PI 295843 and PI 299318 selections were also not infected. Infection rates in susceptible checks ranged from 22.5% to 47.6% and from 0 to 13.9% among triploids. Both ploidy level and genotype significantly affected infection rates. Infestation rates in triploid seeds were reduced but not eliminated by dry heat up to 75C. Heat treatment necessary to kill the pathogen was detrimental to germination.
The cost-effectiveness of using winter cover crops to reduce nitrogen leaching was estimated. Costs were based on cucumber and sweetpotato grown in rotation, three fertilizer application levels (0, 60, and 120 kg N/ha), and three winter covers (weeds/bare, wheat, and clover). Soil N was measured in 15-cm intervals to a depth of 90 cm at the 1993 harvest and 1994 planting. The cover crop biomass was also analyzed. Nitrogen trapping by wheat and clover was compared to bare ground with adjustment for N fixing by clover. Four scenarios—sweetpotato/both covers/high N and cucumber/wheat cover/low and medium N—yielded increased leaching compared to their bare ground counterparts. Leaching prevented from the other scenarios ranged from 1.07 to 20.11 kg·ha–1. Costs, yields, and vegetable prices were used to calculate profit changes from the bare ground method on a dollar/kg basis. Profit changes ranged from negative $2372.74/kg for cucumber/wheat cover/high fertilizer to the only positive change of $16.53 for sweetpotato/clover/medium fertilizer. Negative costs resulted from yield increases when nonwinter weed covers were used.