Comparative effectiveness of commercial tomato rootstocks to control bacterial wilt

Bacterial wilt, caused by Ralstonia solanacearum, is one of the main diseases of solanaceous crops in Tropical regions, being the major limiting factor for tomato production in the North Region of Brazil. The disease has also been a constraint to tomato production under protected cultivation, which had solid expansion in the South and Southeast regions in the last decades. Although sources of resistance to bacterial wilt have been identified in S. lycopersicum germplasm, no resistant cultivars are available to growers. However, commercial rootstocks are available to protect scions against the disease, thus reducing the incompatibility associated to the use of different Solanaceae species/genera. The main objective of the present work was to evaluate the levels of resistance of a group of commercial hybrid/inbred tomato rootstocks to a diverse array of five R. solanacearum isolates (all obtained from infected tomato plants). A clear discrimination was observed among the evaluated rootstocks in relation to disease incidence. The phenotypic reaction of the tomato rootstocks was isolate-specific. The tomato hybrids 'Muralha' and 'Guardião' and the inbred line 'Hawaii 7996' (international resistance standard) were the rootstocks with best performance against the majority of the five R. solanacearum isolates, displaying significantly better resistance when compared with the hybrids 'Magnet' and 'Protetor'. However, all rootstocks were highly susceptible (100% mortality) to the R. solanacearum CNPH 488 isolate (classified as race 1 / Biovar 2, collected in Paraná State, Brazil). The same set of rootstocks was also evaluated under artificially infested soil (with less intense inoculum pressure). The hybrids 'Guardião' and 'Muralha' repeated their good performance when compared with 'Magnet' and 'Protetor'. Our results reinforce the notion that under favorable environmental conditions and/or in the presence of highly virulent strains, the system based upon tomato scion grafted onto tomato rootstock might provide unsatisfactory levels of bacterial wilt control. Therefore, complementary and preemptive control measures will be necessary in order to reduce the initial inoculum pressure in the soil.

由青枯雷尔氏菌（Ralstonia solanacearum）引发的青枯病，是热带地区茄科作物的主要病害之一，同时也是巴西北部地区番茄生产的核心限制因素。该病害亦对保护地番茄生产构成制约，近几十年来，保护地番茄在巴西南部与东南部地区实现了迅猛扩张。尽管科研人员已在栽培番茄（S. lycopersicum）种质资源中鉴定出抗青枯病的材料，但目前尚无可供种植者使用的抗病栽培品种。不过，当前已有商用砧木可用于保护接穗免受该病害侵害，进而降低了使用不同茄科物种/属时伴随的嫁接不相容性问题。本研究的核心目标为：评估一组商用杂交/自交系番茄砧木对5株不同来源的青枯雷尔氏菌分离物（均从染病番茄植株中分离得到）的抗性水平。研究结果显示，在供试砧木间可清晰区分出不同的病害发病率水平；番茄砧木的表型反应具有分离物特异性。番茄杂交种‘穆拉利亚’（Muralha）、‘瓜迪亚昂’（Guardião）以及自交系‘夏威夷7996’（国际抗性标准参照材料）是对5株青枯雷尔氏菌分离物中多数菌株表现最优的砧木，其抗性显著优于‘马格纳特’（Magnet）与‘普罗泰托尔’（Protetor）杂交种。然而，所有供试砧木对青枯雷尔氏菌CNPH 488分离物（归类为1号小种/生物型2，采集自巴西巴拉那州）均表现为高度感病（死亡率达100%）。研究团队还在接种物压力较低的人工接种土壤中，对同一组砧木材料进行了抗性评估，结果显示‘瓜迪亚昂’与‘穆拉利亚’再次展现出相较于‘马格纳特’和‘普罗泰托尔’更优异的抗性表现。本研究结果进一步证实：在环境条件适宜或存在强致病力菌株时，番茄接穗嫁接至番茄砧木的体系对青枯病的防控效果或难以达到理想水平。因此，为降低土壤中的初始接种物压力，需采取补充性与预防性的防控措施。