Photosynthetic Gas Exchange in Common Bean Submitted to Foliar Sprays of Potassium Silicate, Sodium Molybdate and Fungicide and Infected with Colletotrichum lindemuthianum

摘要

This study investigated whether foliar sprays of potassium silicate (KSi), sodium molybdate (NaMo) or a combination of both (KSi+NaMo), with or without the fungicide azoxystrobin (Azox), could reduce anthracnose symptoms, improve photosynthesis and increase yield. Two 2x4 factorial experiments, consisting of untreated or fungicide-treated plants sprayed with KSi, NaMo or KSi+NaMo were arranged in a randomized block design with three replications. The treatments were as follows: (i) KSi; (ii) NaMo; (iii) KSi+NaMo; (iv) Azox; (v) Azox+KSi; (vi) Azox + NaMo; (vii) Azox+KSi + NaMo; and (viii) control (no KSi, NaMo or Azox). The KSi, NaMo and Azox treatments were applied at the rates of 35g/l, 90g/ha and 120gai/ha, respectively. KSi was applied at 20, 27, 40 and 55days after sowing (das). NaMo was applied only at 27das, whereas the fungicide was applied at 27, 40 and 55das. The plants were inoculated with Colletotrichum lindemuthianum at 23das. The anthracnose severity was reduced by 64.25% and yield increase by 156.2% in plants sprayed with fungicide compared with non-sprayed ones. The KSi, NaMo and NaMo + KSi applications reduced anthracnose severity by 31.8, 16.1 and 37.9%, respectively, while the yield increased by 16.8, 18.9 and 63.9%, respectively. There was no difference between treated and non-treated plants with KSi with respect to the leaf gas exchange parameters C-i, E and g(s). However, A significantly increased by 16.9% in plants treated with Azox. The A was not affected by KSi or NaMo spray; however, it was significantly increased by 12.5% after spraying with NaMo + KSi. In conclusion, bean plants treated with Si and Mo were associated with a decrease in anthracnose as well as an enhancement in photosynthesis activity under field conditions.