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

This study investigated whether foliar sprays of potassium silicate ( KS i), sodium molybdate (NaMo) or a combination of both ( KS i + NaMo), with or without the fungicide azoxystrobin (Azox), could reduce anthracnose symptoms, improve photosynthesis and increase yield. Two 2 × 4 factorial experiments, consisting of untreated or fungicide‐treated plants sprayed with KS i, NaMo or KS i + NaMo were arranged in a randomized block design with three replications. The treatments were as follows: (i) KS i; (ii) NaMo; (iii) KS i + NaMo; (iv) Azox; (v) Azox + KS i; (vi) Azox + NaMo; (vii) Azox + KS i + NaMo; and (viii) control (no KS i, NaMo or Azox). The KS i, NaMo and Azox treatments were applied at the rates of 35 g/l, 90 g/ha and 120 g ai/ha, respectively. KS i was applied at 20, 27, 40 and 55 days after sowing (das). NaMo was applied only at 27 das, whereas the fungicide was applied at 27, 40 and 55 das. The plants were inoculated with Colletotrichum lindemuthianum at 23 das. 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 KS i, NaMo and NaMo + KS i 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 KS i 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 KS i or NaMo spray; however, it was significantly increased by 12.5% after spraying with NaMo + KS i. 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.