Thermal stress alleviating potential of endophytic fungus rhizopus oryzae inoculated to sunflower (helianthus annuus L.) and soybean (glycine max L.)

Agricultural crops including sunflower and soybean are facing thermal stress because of rapid change in climate caused by global warming. Some innovative steps should be taken on an emergency basis to prepare plants for such unfriendly stressful conditions. Use of endophytic fungi might be one of the successful weapons to protect food crops, susceptible to high temperature. These endophytes are known to secrete vital stress responsive secondary metabolites that not only provide resistance to crops against abiotic stresses but also help in promoting plants-growth and yield. Therefore, endophytic fungi were isolated from the leaves and roots of Adiantum capillus-veneris L. and their potential were checked for secreting bioactive secondary metabolites and possessing plant-growth promoting potential. A high concentration of phenolics, flavonoids, salicylic acid (SA) and indole 3-acetic acid (IAA) were found in the culture filtrate of isolate AdR-1, thus confirming their growth promoting potential for plants. Later on, phylogenetic exploration and 18S rDNA sequence homology showed that the selected isolatic fungus is Rhizopus oryzae. This strain was inoculated to sunflower and soybean seedlings exposed to normal (25°C) and high (40°C) temperature stress in a growth chamber and their potential for thermal stress resistance was compared with control seedlings. Inoculated sunflower and soybean plants had shown low level of abscisic acid (ABA) while, high levels of ascorbic acid oxidase (AAO), catalase (CAT), proline, phenolics, flavonoids, sugars, proteins and lipids were noted. The endophytic fungus was also found stimulatory to chlorophyll content, shoot and root lengths, fresh and dry biomass as compared to un-inoculated plants. These results confirmed the beneficial role of R. oryzae for crop plants under thermal stress and suggested their use for sustainable agriculture in the future. (author)