Diagnóstico molecular y control biológico de la tristeza seca del pimiento y la fusariosis vascular del melón

The southeast Spain is localized in an area with an important agricultural sector that is well-known for its high production of pepper and melon. These two crops are affected by Phytophthora root rot and Fusarium wilt, respectively. An early detection of the causal agents of these diseases is of paramount relevance to avoid their expansion in new fields and, to improve the management strategies for their control. For this reason, we developed a TaqMan system in order to detect and quantify Phytophthora nicotianae specifically by real time PCR (qPCR) in pure culture and environmental matrices such as soil, compost and plant tissues. With this system, we identified P. nicotianae as the current causal agent of Phytophthora root rot in El Campo de Cartagena and we characterized its population through the use of mitochondrial molecular markers and phenotypic traits. Moreover, the application of the TaqMan system along with a new approach, namely digital PCR (dPCR), proved to be an attractive alternative to quantify P. nicotianae accurately. The dPCR was not only able to detect the presence of low levels of P. nicotianae in environmental samples, but was also less susceptible than the qPCR to inhibitors present in the DNA plant extracts. We also evaluated the ability of a batch of composts made from agro-industrial waste to control Fusarium wilt and Phytophthora root rot under greenhouse nursery conditions. The results showed positive correlations between enzymatic activities such as NAGase, chitinase and protease regarding Fusarium wilt suppression, and dehydrogenase activity related to Phytophthora root rot suppression. Besides, a deeper study was carried out in order to elucidate the mechanisms involved in Phytophthora root rot control. This was accomplished studying the physical and chemical characteristics of composts, including their organic matter composition, and analyzing their metagenome and metabolome. We observed that the involvement of certain antagonistic microbes such as Streptomyces, Bacillus, Zopfiella or Fusarium in the phenomenon of disease suppression was related to the degree of stabilization of the materials and thus, to the microbial activity achieved. These parameters provided an array of outcomes whose integration may be a promising approach to improve not only the characterization but also the identification of suppressive composts. Furthermore, vineyard pruning waste compost amended with Trichoderma hazianum showed better results controlling Fusarium wilt than the same compost without this BCA and compared with peat. The control exerted by T. harzianum itself as well as the changes induced by its presence in the bacterial community and in some chemical parameters may explain these results. The use of composts fortified with certain strains of BCA can be a good alternative controlling Fusarium wilt of melon seedlings at greenhouse nursery level. The use of in vivo tests to characterize the suppressive effect of composts was vital to obtain accurate conclusions due to the inability of in vitro tests to provide them.