不同发酵条件对瓜类细菌性果斑病菌感染西瓜种子的影响

Effects of different fermentation conditions on Acidovorax citrulli infestation of watermelon seeds

西(甜)瓜果斑病是西瓜嗜酸菌Acidovorax citrulli侵染瓜类作物引起的典型细菌病害,种子带菌是该病最重要的传播方式,防止种子感染是病害预防的首要环节。本研究分析了西瓜种子不同发酵条件对种子感染病菌的影响。研究通过人工接种西瓜发酵液,设置发酵温度为20℃和30℃,检测在不同发酵时间下发酵液pH、A.citrulli菌量、种子外部带菌量、种子内部带菌率,以及出苗发病率,系统地分析比较发酵条件对西瓜嗜酸菌侵染种子的影响。结果表明:从开始发酵到发酵24h,发酵液中A.citrulli菌量快速增长并达到峰值1011cfu/mL,随后逐渐减少;发酵24h的种子外部带菌量最高,达到4×109 cfu/mL;发酵过程中A.citrulli可侵染种皮内部(10%)及种仁(1%);发酵温度对种子感染A.citrulli及幼苗发病率的影响不显著;此外,发酵液菌量与pH相关性显著。以上研究结果表明:控制发酵温度并不能够减少A.citrulli菌的种子感染,减少发酵时间才是减少病菌增殖感染种子的防控关键。

Acidovorax citrulli,a typical seed-borne bacterial pathogen,can infect many cucurbitaceous crops.Preventing seed infestation plays the first key role in disease management.This study analyzed the effects of fermentation conditions on A.citrulli infestation of watermelon seeds.Watermelon seeds were fermented under two temperatures（20℃,30℃）in inoculated watermelon fermentation liquid.The fermentation liquid sample and seed sample were taken at different fermentation time points for the measurement of pH,bacterial cell density in the fermentation liquid,and detection of external/internal seed infestation,as well as the evaluation of seedling disease incidence.The effects of fermentation conditions on watermelon seed infestation by A.citrulli were systematically compared and analyzed.The results showed that A.citrulli in fermentation liquid proliferated rapidly and cell density reached the peak of 10^（11） cfu/mL at the first 24 h of fermentation,and then declined gradually.The maximum amount of A.citrulli on the exterior of seeds fermented for 24 h was 4×10~9 cfu/mL,and infestation of the interior of the seed coat（10%）and embryo（1%）were also observed in 24 h.However,fermentation temperature affected neither the seed infestation of A.citrulli significantly,nor the seedling disease incidence.Additionally,the bacterial amount was significantly correlated with pH value in the fermentation liquid.The present study indicated that controlling fermentation temperature could not reduce the seed infestation of A.citrulli.The reduction of fermentation time is a key factor for inhibiting bacterial cell growth and preventing seed infestation.