Crotalaria species in succession to soybean for the management of Pratylenchus brachyurus

ABSTRACT: Soybean is the main agricultural crop in the State of Mato Grosso do Sul, Brazil. It is primarily cultivated in a crop succession system, in wich soybean is grown in spring/summer, followed by corn or graminaceous pastures in autumn/winter as a second crop. Due to the intensive cultivation, new phytosanitary problems have arisen, among them the root-lesion nematode, Pratylenchus brachyurus, which besides causing damage to plant roots, can be important gateway for other soil pathogens. The recent occurrence of high nematode population densities has brought great concern due to the limited resistant soybean genotypes available. Besides, the use of nematicides only reduces nematodes populations temporarily. A viable alternative for the control of soil nematodes could be the use of Crotalaria spp. in succession or rotation with soybean. Crotalaria is immune or a bad host to the nematode, besides having high capacity of biological nitrogen fixation. Thus, the objective of the present research was to define the best way of insertion of this legume as a second crop in soybean production systems to reduce the population density of the root-lesion nematode. Two experiments were carried out: one in the field, in an infested area, and other in a greenhouse. In both experiments, the treatments were: 1) Zea mays, 2) Brachiaria brizantha cv. Xaraés,, 3) Z. mays + Crotalaria spectabilis, 4) Z. mays + C. ochroleuca, 5) B. brizantha cv. Xaraés + C. spectabilis, 6) B. brizantha cv. Xaraés + C. ochroleuca, 7) C. spectabilis, and 8) C. ochroleuca. The effect of the treatments was evaluated by estimating the number of nematodes in the roots of autumn/winter crops, as well as in the roots of the soybean cultivated in the sequence. The cultivation of both Crotalaria species provided suppression of the nematode population. However, when intercropped with corn or Xaraés palisade grass, the suppressive effect of Crotalaria was supplanted by corn and Xaraés palisadegrass susceptibility to the root-lesion nematode.

摘要：巴西南马托格罗索州的主栽农作物为大豆。当地主要采用作物接茬种植模式：春夏季种植大豆，秋冬季以玉米或禾本科牧草作为后茬作物。由于集约化种植，当地出现了新的植物保护相关问题，其中包括短尾根腐线虫（Pratylenchus brachyurus）：该线虫不仅会损伤植物根系，还可成为其他土壤病原物的重要侵染途径。近期该线虫种群密度居高不下，引发了广泛担忧，原因是可用的抗线虫大豆基因型十分有限。此外，杀线虫剂仅能暂时降低线虫种群数量。针对土壤线虫防控，一种可行的替代方案是将猪屎豆属（Crotalaria spp.）植物与大豆进行接茬种植或轮作。猪屎豆属植物对该线虫具有免疫性或为非寄主，同时具备极强的生物固氮能力。因此，本研究旨在明确该豆科植物作为大豆生产体系中后茬作物的最佳种植方式，以降低短尾根腐线虫的种群密度。

本研究共开展两组试验：一组为田间试验，设置于线虫侵染区域；另一组为温室盆栽试验。两组试验的处理组均设置如下：1）玉米（Zea mays）；2）Xaraés品种臂形草（Brachiaria brizantha cv. Xaraés）；3）玉米+美丽猪屎豆（Crotalaria spectabilis）；4）玉米+黄花猪屎豆（Crotalaria ochroleuca）；5）Xaraés品种臂形草+美丽猪屎豆；6）Xaraés品种臂形草+黄花猪屎豆；7）美丽猪屎豆；8）黄花猪屎豆。

本研究通过计数秋冬季作物根系以及后续种植大豆的根系中的线虫数量，评估各处理组的防控效果。结果显示，两种猪屎豆属植物的单一种植均能有效抑制线虫种群。但当与玉米或Xaraés臂形草间作时，猪屎豆的抑线虫效果会被二者对短尾根腐线虫的敏感性所抵消。