Effect of Mycorrhizal Infection on Phosphorus Efficiency of Maize (Zea mays L.) Cultivars

Phosphorus is considered as one of the least available plant nutrients found in the rhizosphere. The large variation in phosphorus acquisition efficiency of different crop cultivars provides opportunities for screening cultivars that perform well on low phosphorus soil for sustainable agriculture. To assess phosphorus efficiency of maize cultivars viz.: Paras and JH 3459, a field experiment was conducted for 2 years at Indian Institute of Technology, Kharagpur, India on sandy loam soil, having pH 5.1, organic carbon 4.1 g kg(-1) soil and as low as 11.2 kg ha(-1) available phosphorus. Phosphorus was applied at a rate of 0 (low) and 400 kg ha(-1) (high) with and without the application of fungicide Benomyl at 500 kg ha(-1) for eradication of arbuscular mycorrhiza. Maize plants were harvested at 24, 48, and 74 days after sowing and final harvest was taken at maturity. In low phosphorus soil without Benomyl, cv. Paras produced 29, 18, and 69 %, while cv. JH 3459 produced 19, 9, and 57 % of their maximum shoot dry weight at 24, 48, and 74 days after sowing, respectively during the first year and the trend was same during the second year. The results indicate that relative shoot dry weight varies with growth stages and therefore, grain yield should be used to assess phosphorus efficiency. At maturity, maize cv. Paras produced 91 and 80 % while JH 3459 produced 71 and 60 % of their maximum grain yield during the first and second year respectively, proving that cv. Paras was more phosphorus efficient than cv. JH 3459. Root growth of both the cultivars was restricted under phosphorus deficiency conditions; however, cv. Paras produced 1.4-2.6 times more root length than cv. JH 3459 at different growth stages. Cultivar Paras had lower phosphorus influx than cv. JH 3459, but it was more phosphorus efficient because of more roots, lower internal phosphorus requirement and higher root length/shoot dry weight ratio. Application of Benomyl was completely effective in suppressing arbuscular mycorrhiza infections up to 48 days after sowing. Its effect started diminishing thereafter and some infection occurred, which however was significantly less than that observed in untreated plots. Thus, the yield difference between Benomyl treated and untreated plots can be attributed to arbuscular mycorrhiza. In low phosphorus soil, Benomyl application reduced the growth of cultivars by 12-45 % and the maximum reduction of growth was at 48 days after sowing. However, in high P soil, Benomyl application had no significant effect on dry matter yield of the cultivars.