Hountondji Fabien C C, Sabelis Maurice W, Hanna Rachid, Janssen Arne
International Institute of Tropical Agriculture, 08 BP 0932, Cotonou, Republic of Benin.
J Chem Ecol. 2005 May;31(5):1003-21. doi: 10.1007/s10886-005-4244-2.
A large body of evidence shows that plants release volatile chemicals upon attack by herbivores. These volatiles influence the performance of natural enemies. Nearly all the evidence on the effect of plant volatiles on natural enemies of herbivores concerns predators, parasitoids, and entomophagous nematodes. However, other entomopathogens, such as fungi, have not been studied yet for the way they exploit the chemical information that the plant conveys on the presence of herbivores. We tested the hypothesis that volatiles emanating from cassava plants infested by green mites (Mononychellus tanajoa) trigger sporulation in three isolates of the acaropathogenic fungus Neozygites tanajoae. Tests were conducted under climatic conditions optimal to fungal conidiation, such that the influence of the plant volatiles could only alter the quantity of conidia produced. For two isolates (Altal.brz and Colal.brz), it was found that, compared with clean air, the presence of volatiles from clean, excised leaf discs suppressed conidia production. This suppressive effect disappeared in the presence of herbivore-damaged leaves for the isolate Colal.brz. For the third isolate, no significant effects were observed. Another experiment differing mainly in the amount of volatiles showed that two isolates produced more conidia when exposed to herbivore-damaged leaves compared with clean air. Taken together, the results show that volatiles from clean plants suppress conidiation, whereas herbivore-induced plant volatiles promote conidiation of N. tanajoae. These opposing effects suggest that the entomopathogenic fungus tunes the release of spores to herbivore-induced plant signals indicating the presence of hosts.
大量证据表明，植物在受到食草动物攻击时会释放挥发性化学物质。这些挥发物会影响天敌的行为。几乎所有关于植物挥发物对食草动物天敌影响的证据都涉及捕食者、寄生蜂和食虫线虫。然而，其他昆虫病原体，如真菌，尚未针对它们利用植物传递的关于食草动物存在的化学信息的方式进行研究。我们测试了这样一个假设：受绿螨（Mononychellus tanajoa）侵染的木薯植株释放的挥发物会触发杀螨真菌新塔螨霉（Neozygites tanajoae）的三个分离株产生孢子。试验在最适合真菌产孢的气候条件下进行，这样植物挥发物的影响只会改变分生孢子的产生量。对于两个分离株（Altal.brz和Colal.brz），发现与清洁空气相比，来自清洁、离体叶盘的挥发物会抑制分生孢子的产生。对于分离株Colal.brz，在存在食草动物损伤叶片的情况下，这种抑制作用消失。对于第三个分离株，未观察到显著影响。另一个主要在挥发物量上有所不同的实验表明，与清洁空气相比，当暴露于食草动物损伤的叶片时，两个分离株产生了更多的分生孢子。综合来看，结果表明来自清洁植物的挥发物会抑制孢子形成，而食草动物诱导的植物挥发物会促进新塔螨霉的孢子形成。这些相反的影响表明，昆虫病原真菌根据食草动物诱导的植物信号（表明宿主的存在）来调节孢子的释放。
