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Compost sustaining a multitude of chitinase-producing bacteria was evaluated in a greenhouse study as a soil amendment for the control of late blight (Phytophthora capsici L.) in pepper (Capsicum annuum L.). Microbial population and exogenous enzyme activity were measured in the rhizosphere and correlated to the growth and health of pepper plant. Rice straw was composted with and without a chitin source, after having been inoculated with an aliquot of coastal area soil containing a known titer of chitinaseproducing bacteria. P. capsici inoculated plants cultivated in chitin compost-amended soil exhibited significantly higher root and shoot weights and lower root mortality than plants grown in pathogen-inoculated control compost. Chitinase and b-1,3-glucanase activities in rhizosphere of plants grown in chitin compost-amended soil were twice that seen in soil amended with control compost. Colony forming units of chitinase-producing bacteria isolated from rhizosphere of plants grown in chitin compost-amended soil were 10 3 times as prevalent as bacteria in control compost. These results indicate that increasing the population of chitinase-producing bacteria and soil enzyme activities in rhizosphere by compost amendment could alleviate pathogenic effects of P. capsici.

Although, considerable differences in root size in response to nitrogen (N) application among crop species and cultivars have been widely reported, there has been limited focus on the differences in root N uptake ability. In this study, two maize (Zea mays L.) hybrids, Zhenghong 311 (ZH 311, N-efficient) and Xianyu 508 (XY 508, N-inefficient), were used to compare differences in root N uptake ability. The two cultivars were grown in field pots Experiment I (Exp. I) and hydroponic cultures Experiment II (Exp. II) supplemented with different concentrations of N fertilizer. In both experiments, the levels of accumulated N were higher in ZH 311 than in XY 508 under low- and high-N supply, and the increment in accumulated N was greater under N deficiency. The maximum N uptake rate (Vm) and average N uptake rate (Va) in Exp. I, the root N kinetic parameter maximum uptake rate (Vmax) per fresh weight (FW) and Vmax per plant in Exp. II, and the root N uptake rate in both experiments were significantly higher for ZH 311 than for XY 508. In contrast, the root-to-shoot N ratio in both experiments and the root N kinetic parameter Michaelis constant (Km) in in Exp. II were markedly higher in XY 508 than in ZH 311, particularly under N-deficient conditions. Higher root N kinetic parameters Vmax per FW and Vmax per plant and lower Km values contributed to higher N affinity and uptake potential, more coordinated N distribution in the root and shoot, and higher root N uptake rates throughout the growth stages, thus enhancing the N accumulation and yield of the N-efficient maize cultivar. We conclude that the N uptake ability of roots in the N-efficient cultivar ZH 311 is significantly greater than that in the N-inefficient cultivar XY 508, and that this advantage is more pronounced under N-deficient conditions. The efficient N acquisition in ZH 311 is due to higher N uptake rate per root FW under optimal N conditions and the comprehensive effects of root size and N uptake rate per root FW under N deficiency.

Plant-parasitic nematodes are distributed worldwide and affect a broad range of important agronomic plant species. Chitinolytic bacteria were evaluated as potential biological control agents of the root-knot nematode, Meloidogyne incognita, on tomato. After transplantation of seedlings into pots containing soil amended with chitin compost, chitin broth, or respective controls, soil was inoculated with nematode eggs and infective second-stage juveniles (J2). Samples taken at 4, 6 and 8 weeks after inoculation indicated that fresh weights of plants did not vary between treatments or between treatments and controls. The gall index was lower in the plants grown in the chitin-amended soil at each time point. Activities of soil chitinase and β-1,3-glucanase were greater in those soils amended with chitin compost and chitin broth. Gall index of tomato root was negatively correlated with soil chitinase activity. Activities of tomato root chitinase and β-1,3-glucanase were higher in plants growing in non-chitin-amended soil at 6 and 8 weeks after nematode infestation. Chitinase activity in tomato root was positively correlated with the gall index of tomato root. The results indicate the potential of chitinase producing bacteria to alleviate nematode parasitism in important vegetable crops.

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