Evaluation of the Effect of Seed Treatments, Bactericides, and Cultivars on Bacterial Leaf Spot of Lettuce Caused by Xanthomonas campestris pv. vitians

Abstract

As a part of a broader program for management of bacterial leaf spot, the effects of lettuce-seed treatments, greenhouse application of bactericides, and cultivars were evaluated. Seed artificially inoculated with Xanthomonas campestris pv. vitians was treated with bactericides or heat treated and evaluated for the incidence of contaminated seed and seed germination. Seed soaked in 1% sodium hypochlorite for 5 and 20 min had an incidence of contaminated seed of less than 10%. Dry-heat (1 h), hot-water (50°C, 2 h), and organic-acid treatments significantly reduced seed germination. Considering both the effects on incidence of contaminated seed and seed germination, the best treatments were soaking the seeds in 1% sodium hypochlorite for 5 or 20 min. Copper sulfate, alone or mixed with Zineb or Dithane, failed to control the disease and caused phytotoxicity. All of the other bactericides significantly reduced the severity of bacterial leaf spot. However, the differences among bactericide efficacy were too small to allow comparison between the different forms of copper used, as well as the effect of adding manganese and zinc (Dithane) or zinc alone (Zineb) to the copper product. Nevertheless, copper hydroxide alone, mixed with Zineb or mixed with Dithane, and basic copper sulfate reduced disease severity by 86.89, 78.67, 80.42, and 81.82%, respectively, without causing phytotoxicity. For the two years of cultivar evaluation, no significant difference in mean disease severity was observed among the cultivars. Based on disease incidence, the most susceptible cultivar was Bellagreen. Cvs. Ideal cos, Grand Teton, Great Lakes, Paris Island, Ithaca, and Optima showed intermediate susceptibility, and the least-susceptible cultivars were Waldmann's and Grand Rapids, both green-leaf type. There was no significant difference between the three romaine (cos) cultivars and between the two crisphead cultivars, but a significant difference was observed between the two butterhead types, Bellagreen and Optima, which had 80.04 and 48.01%, respectively, of their leaves diseased at the time of harvest.

Sheath Brown Rot Disease of Rice Caused by Pseudomonas Fuscovaginae in the Peninsular Malaysia

“…Klement et al (1990) stated that the use of resistant variety for the disease control was the most effective. Earlier findings by Macapuguay and Mnzaya (1988), Sharma et al (1997) and Carisse et al (2000) also showed that planting of a few selected varieties could control or at least reduce the infection in the field.…”

Bacterial leaf spot, a new disease of lettuce in Quebec caused by Xanthomonas campestris pv. vitians

“…The most efficient treatment was 1% of sodium hypochlorite for a soaking time of 5 to 20 min. However, treatments using dry heat or hot water for more than 1 h reduced significantly the seed germination as compared to the untreated seeds (Carisse et al 1999).…”

“…For instance, in Butterheads, the cultivar Bella Green was highly susceptible and the cultivar Optima showed a low disease severity. Nevertheless, symptoms of BLSL were observed in ail cultivars tested, but the green leaf types were the least susceptible (Carisse et al 1999).…”

“…Pesticides allowed on other vegetables for control of bacterial diseases were tested for the control of bacterial leaf spot of lettuce. The most efficient treatments reduce disease severity by only 50% of that observed on non-treated plants (Carisse 1997;Carisse et al 1999;Toussaint et al 1998aToussaint et al , 1999a. Moreover, the use of some copper bactéricides caused symptoms of phytotoxicity on lettuce plants.…”

Evaluation of susceptibility of an olive progeny (Picholine x Meski) to olive leaf spot disease caused by Fusicladium oleagineum

“…Application of copper-based fungicides is now the main method of olive leaf spot control in Tunisia and other olive growing countries. However, although there is a lower risk of pathogens developing resistance to copperbased fungicides since they have multi-site activity, some cases of resistance have been reported in bacterial diseases (Vanneste et al 2003;Carisse et al 2000). Washington et al (1992) have reported that copper hydroxide has been ineffective on grey mould of strawberries.…”