(64(2):89-98)Effect of Temperature on Virulence of Ralstonia solanacearum Biovars and Response of Potato Cultivars (Lines) to Bacterial Wilt

Abstract

青枯病菌 (Ralstonia solanacearum) 引起之細菌性萎凋病為熱帶及亞熱帶地區作物關鍵病害之一。多數青枯病菌株於高溫對寄主具有病原性，部分菌株在20℃以下則會失去其病原性。然而，分類上屬於第三生理小種、第二生化型 (R3Bv2) 的菌株於冷涼的溫度條件下仍可感染寄主植物，造成病害。本研究中調查2013 年11月至2014年3月期間，台灣雲林縣及嘉義縣馬鈴薯栽培區萎凋病之發病率為0–32%，分離其病原菌，發現皆為青枯病菌，其中64.7% 之分離株為第二生化型之菌株，其餘為第三生化型之菌株，顯示青枯病菌第二生化型之菌株為目前危害台灣馬鈴薯之主要菌株。此外，亦於不同溫度下比較台灣常見3 種R. solanacearum生化型菌株對茄科作物之致病力差異。結果顯示在24℃及28℃，3 種生化型菌株 (RS1102、RS1118 及RS1125)皆對試驗植物具有良好的致病力，接種後20 d 罹病度 (disease severity) 介於77–100%。但於20℃時，RS1125(第三生化型) 則對馬鈴薯失去其病原性，而RS1118 (第二生化型) 則表現較其他兩種生化型菌株較強之毒力，接種20 d 後馬鈴薯及番茄上之罹病度為80–100%。青枯病為馬鈴薯生產栽培之限制因子之一，故本研究利用10 種不同之馬鈴薯品種 (系) [P86 (「克尼伯」)、P90 (「大西洋」)、P91 (「種苗2 號」)、P92 (「吉比 達」)、P95 (‘pike’)、P117 (‘Chipeta’，「聯華」)、P120 (「台農1 號」)，P89、16-13 及T3] 針對第二生化型之菌株進行抗病分析，以期篩選對青枯病具有抗性之品種。結果顯示，品種間表現出不同程度之耐性，但未獲得表現高抗 (無萎凋) 之抗病品種。接種35 d 後，品種間罹病度為10–100%，其中以T3 品種之罹病度最低。經上述試驗結果可知，溫度為影響青枯病發病率之因素之一，台灣常見之3 種青枯病菌生化型菌株中，則以第二生化型菌株在低溫時對馬鈴薯之危害程度為最高、威脅性最大。 Bacterial wilt, caused by Ralstonia solanacearum, is an important disease of a wide range of crops in tropical and subtropical regions. Most strains of R. solanacearum are pathogenic at high temperatures, and some strains are nonpathogenic when the temperature drops below 20℃. However, race 3 biovar 2 (R3Bv2) strains can attack plants at cool temperatures. In this study, we surveyed the potato fields in Yunlin and Chiayi Counties in Taiwan during 2013–2014 and observed the incidences of wilting symptoms on potato, within 0–32%. The causal pathogens were identified and most of the stains were identified to be R. solanacearum biovar 2, indicating that the biovar 2 is a dominant strain to affect potato in Taiwan. In addition, the effects of temperature on the virulence of three R. solanacearum strains (RS1102, RS1118 and RS1125) and the representative biovars affecting solanaceous crops in Taiwan were evaluated on potato and tomato plants, respectively. Results indicated that all three strains showed strong virulence on potato and tomato plants at 24℃ and 28℃, and the disease severity ranged from 77 to 100% at 20 days of post inoculation. At 20℃, the three strains showed differential reactions on the inoculated potato. Among them, RS1125 (biovar 3) was nonpathogenic to potato, whereas RS1118 (biovar 2) showed higher virulence than the other two strains with 80–100% disease severity at 20 days of post inoculation. To compare the resistance between the current commercial potato cultivars to R. solanacearum race 3 biovar 2, ten cultivars [P86 (‘Kennebec’), P90 (‘Atlantic’), P91 (‘Tss-II’), P92 (‘Chipeta’), P95 (‘pike’), P117, P120 (‘TN-1’), P89, 16-13, and T3] were examined in this study. It indicated a differential susceptibilities among them, from susceptible to various degrees of tolerance, to the infection of R. solanacearum race 3 biovar 2. The disease severity ranged between 10–100% at 35 days of post inoculation. One cultivar, T3, showed the lowest disease severity at 10%. No cultivar exhibited immunity to the bacterium. Based on our results, we concluded that temperature is one of the factors that can affect the virulence of R. solanacearum. Comparing the virulence of three commonly found biovars of R. solanacearum in Taiwan at different temperatures, we suggest that bovar 2, which showed high virulence at cool temperatures, might be a great threat to the potato production in Taiwan