EVALUATION ON FIELD TRIALS OF DIFFERENT INOCULATION STRATEGIES OF Bacillus SP. CHEP5 TO INDUCE THE DEFENSE RESPONSE OF PEANUT CROP AGAINST Thecaphora frezii.

FIGUEREDO, MARÍA SOLEDAD; TONELLI, MARÍA LAURA; LOSER, URSULA; KEARNEY, MARCELO; ZUZA, MÓNICA; PERALTA, V; RAGO, ALEJANDRO; FABRA, ADRIANA

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Fungal diseases are a major limitation in peanut production. One of the diseases of great importancein Argentina is peanut smut, caused by the fungus Thecaphora frezii. To date, there is no efficientcontrol strategy for this pathogen. The use of biocontrol agents represents an alternative for thepeanut smut management. The antagonistic effect of these agents may be mediated by ISR (InducedSystemic Resistence). This phenomenon is defined as the physiological state of plants in which theirdefensive capacity against a wide spectrum of pathogens is increased. The aims of this study were toevaluate in field trials: 1. different inoculation strategies of the biocontrol agent Bacillus sp. CHEP5(CHEP5) to select those more effective. 2. If the biocontrol activity was mediated by ISR. Three trialswere carried out in different seasons (2019-2020, 2020-2021 and 2021-2022). The inoculationstrategies evaluated were: 1)-CHEP5 applied to seed (T2), 2)-CHEP5 applied to seed followed by afoliar application at 10 days prior to peg development(T3), 3)- CHEP5 applied to seed and foliarapplication the date of peg development(T4), 4)- foliar application of CHEP5 at 10 days prior to pegdevelopment (T5) and 5)- foliar application of CHEP5 at the date of the peg development (T6).Untreated plots were used as controls (T1). At harvest time, the incidence of peanut smut wasevaluated as a percentage of affected pods, and the severity according to the degree of affectation,using a diagrammatic scale of five degrees (0-4). In addition, from the momento of peg development,systemic tissue samples were taken every 7 days in order to determine the activity of peroxidases(PX) and the content of phenolic compounds(PC).In the first trial (2019-2020), there was a reductionof the smut incidence and severity in plants treated with T2, T3, T4 and T5. Accoding to these results,increased PX activity and PC content were determined in plants from treatments T2, T3 and T4compared to T1. During the second trial (2020-2021), similar values of disease incidence and severity were obtained, standing out T3 and T4 as the best inoculation strategies. These plants also showedan increased PC content compared toT1. In the last trial (2021-2022) there was no reduction inincidence or severity of peanut smut in plants treated with the different inoculation strategiescompared to T1. As expected no increment was registrated in PX activity. However, a slight incrementin the accumulation of PC was observed in plants treated with T2 and T3. We conclude that theapplication of Bacillus sp. CHEP5 to seed, followed by a foliar application at 10 days prior to pegdevelopment represents an effective alternative to control peanut smut. Moreover, this protectionis associated to an increased PX activity and especially to a higher PC accumulation as result of Bacillussp. CHEP5 defense response induction in peanut.