Effects of commercial formulations of Bacillus thuringiensis and Streptomyces avermitilis on Tylenchulus semipenetrans and on nutrition status, yield and fruit quality of mandarin

Abstract

A study was conducted during two successive growing seasons (2007 and 2008) to assess the effects of a commercial formulation (Agerin®) containing an isolate of Bacillus thuringiensis and another, abamectin, containing fermentation products of Streptomyces avermitilis, on the citrus nematode, Tylenchulus semipenetrans, infecting 15-year-old Balady mandarin (Citrus reticulata) trees grafted on sour orange (Citrus aurantium) rootstock. The mandarin was grown in a sandy soil at a tree spacing of 3.5 m × 3.5 m, with drip irrigation and under field conditions. The application rates were 1, 2 and 3 kg/4200 m2 for Agerin® and 5 l/tree of distilled water containing 200, 400 and 800 ppm for abamectin. All treatments suppressed nematode populations with the percentage of reduction being positively correlated with the rate of application. Also, the treatments markedly improved nutritional status, yield and fruit quality. The best nematode control was achieved with the highest rate of Agerin®, which reduced the reproduction rate of the nematode in both seasons (R = 0.16 and 0.15). Similar control was obtained with abamectin, with the highest rate of application resulting in the lowest reproduction rates (R = 0.21 and 0.15 in the two seasons), followed in effectiveness by the intermediate and the lowest rates. The best nutritional status of mandarin trees occurred when the treatments were applied at the highest rates. The treatments increased both macro (N, P, K, Ca and Mg) and micro (Fe, Zn and Mn) nutrient element contents in leaves. The yields increased by 52.9-69.2% and 84.6-115.4% following application of the products at the highest rates in both seasons. It is concluded that Agerin® and abamectin have potential as non-chemical control strategy tools in managing the citrus nematode. These two bioagents also have low associated production costs and are considered to be environmentally safe.