Search for sources of resistance to Meloidogyne enterolobii in commercial and wild tomatoes

ABSTRACT Meloidogyne enterolobii (=M. mayaguensis) is an emerging plant pathogen capable of inducing root galls and yield reduction in a wide range of host species. This pathogen has also been reported as a global threat for tomato (Solanum lycopersicum) crop production mainly due to its ability to overcome the resistance meditated by the Mi-1 gene. Despite the potential importance of this nematode, sources of resistance to M. enterolobii are not yet available for breeding purposes. The main objective of the present work was to evaluate a large Solanum (section Lycopersicum) germplasm (comprising nine species and one botanic variety) aiming to identify useful sources of resistance to M. enterolobii. In the first screening assay, 101 accessions and the susceptible standard S. lycopersicum ‘Santa Cruz’ were inoculated and evaluated under controlled conditions. The phenotypic criteria used for evaluation were the number of root galls, gall index, number of eggs, and the reproduction factor. Plants of the 20 selected accessions were cultivated in 0.4 L pots filled with sterile soil. Inoculation procedures were identical to the first assay, but with higher inoculum pressure (3,300 eggs per plant). Three accessions with superior tolerance levels to M. enterolobii were identified viz. S. lycopersicum ‘Yoshimatsu’, S. lycopersicum ‘CNPH 1246’ and S. pimpinelifolium CGO 7650 (= CNPH 1195). These accessions were re-evaluated against a distinct M. enterolobii population as well as against two other root-knot nematode species (M. javanica and one M. incognita race 1). Under higher inoculum pressure, ‘Yoshimatsu’ was found to be resistant to M. javanica and M. incognita race 1, but susceptible to M. enterolobii from guava. The other two sources displayed susceptibility to all three nematodes. Additional germplasm screening is needed since no source of stable genetic resistance to M. enterolobii was found so far.

摘要：象耳豆根结线虫（Meloidogyne enterolobii），异名马亚格斯根结线虫（M. mayaguensis），是一种新兴植物病原物，可侵染多种寄主植物并诱导根结形成，导致寄主产量下降。该病原物已被证实为全球番茄（Solanum lycopersicum）生产的主要威胁，其核心原因在于它能够突破由Mi-1基因（Mi-1 gene）介导的抗病性。尽管该线虫具有极高的潜在危害性，但目前尚无适用于育种工作的抗象耳豆根结线虫种质资源（germplasm）。本研究的核心目标为评估一份大型茄属（Solanum）番茄组（section Lycopersicum）种质资源库，涵盖9个物种与1个植物变种，以期筛选出可用于抗象耳豆根结线虫育种的有效抗源。

在首轮筛选试验中，研究人员对101份种质材料以及感病对照品种‘圣克鲁斯（Santa Cruz）’番茄进行接种，并在可控环境条件下开展表型评价。本次评价采用的表型指标包括根结数量、根结指数（gall index）、卵粒数量以及繁殖系数（reproduction factor）。研究人员将首轮筛选出的20份种质种植于容积0.4升的无菌土壤盆栽中，接种流程与首轮试验保持一致，但接种压力（inoculum pressure）提升至每株3300粒线虫卵。

最终鉴定出3份对于象耳豆根结线虫具有优异耐性的种质：番茄品种‘吉松（Yoshimatsu）’、番茄品系‘CNPH 1246’以及*S. pimpinelifolium* CGO 7650（=CNPH 1195）。研究人员进一步采用不同的象耳豆根结线虫种群，以及另外两种根结线虫——爪哇根结线虫（M. javanica）和南方根结线虫1号小种（M. incognita race 1）——对这3份种质进行了复筛。在高接种压力条件下，‘吉松’对爪哇根结线虫与南方根结线虫1号小种表现为抗病，但对来自番石榴的象耳豆根结线虫种群表现为感病。其余两份种质对三种供试线虫均表现为感病。截至本研究开展时，尚未发现稳定抗象耳豆根结线虫的遗传资源，因此仍需开展更多的种质筛选工作。