The obtainment of 30 new strains from native Trichoderma harzianum
after UV light irradiation (UV-A and UV-C), and of 82 strains resulted
from protoplast fusion were accomplished. The new strains, initially
selected for their growing rate under low temperature and high pH
conditions, as well as for their innocuousness on tomato plants, were
tested for in vitro inhibition of Pyrenochaeta lycopersici in dual
cultures and due to secretion of volatile and diffusible metabolites.
All the UV-A and UV-C selected candidate mutants were innocuous to
tomato plants, but none of them showed improvement in their biocontrol
activity on P. lycopersici. Th12A20.1 increased 1.3 and 1.9 fold the
total fresh weight of Fortaleza tomato plants when compared to its
parental strains Th12 and Th11, respectively. The selected candidate
mutants obtained through protoplast fusion were also innocuous to
tomato plants, but only ThF1-2 and ThF4-4 inhibited 1.3 fold (in dual
cultures) and 5 fold (due to secretion of volatile metabolites) the
growth of P. lycopersici, respectively, in relation to the mean
inhibitory effect of both parents. Therefore, these candidate mutants
could be included in experiments under field conditions