Colonization pattern of crop plants by endophytic fungi

Endophytes are fungi or bacteria occurring inside plant tissues without causing any apparent symptoms in the host plants. Fungal endophytes are quite common in nature; some of them are able to work as bio-control agents to defend insects, nematodes and plant pathogens. As endophytic fungi can continuously be presented and expressed throughout the crop cycle. Such an endophytic expression of the entomopathogens within the plant system is expected to be more advantageous than external application of bio-agents. Fungi Beauveria bassiana (strain ATP01, ATP02, Bb03032, EABb04/01-tip and Naturalis) and Trichoderma harzianum (strain T39 and Tu) have been already proved and well-studied as endophytes in host plants to work against either herbivores or plant pathogens. This study aimed at introducing B. bassiana and T. harzianum to host plant cabbage and faba bean as endophytes. The distribution of the endophytic fungi was investigated by selective medium re-isolation and q-PCR with the comparison ofdifferent inoculation methods.. Bioassays were conducted to test the influence of the fungal endophytic colonization on herbivores. Main findings: Both B. bassiana and T. harzianum were able to establish in the host plants as endophytes. By different inoculation methods, various colonization patterns were found where B. bassiana had the best fungal establishment in leaf inoculated treatments while T. harzianum had the better performance in below ground inoculated trials (root inoculation and seed inoculation). With root and seed inoculation, both B. bassiana and T. harzianum had a higher colonization level in faba bean compared with cabbage. The existence of endophytic fungi influenced the development and behavior of the diamondback moth (DBM) Plutella xylostella. DBM larvae feeding on detached B. bassiana (strain ATP02) inoculated leaf had a slower development and a lower body weight. In the dual-choice oviposition choice experiments the DBM significantly preferred control plants to B. bassiana inoculated plants. At a high colonization level, endophytic T. harzianum was able to affect both the feeding choice and oviposition choice in the dual-choice bioassays, although T. harzianum could not kill DBM larvae directly and the endophytic T. harzianum also did not affect the DBM larvae development significantly. The endophytic establishment of T. harzianum strongly influenced the volatile emission. The green volatile compounds content decreased while the percentage composition of terpenes increased in T. harzianum inoculated treatments.