Resistência de genótipos de batata (Solanum tuberosum) à requeima (Phytophthora infestans) e à pratilencose (Pratylenchus brachyurus) e ação fungicida e nematicida de formulações a base de quitosana para uso na cultura

Abstract

Looking for alternatives in the management of late blight (Phytophthora infestans) and root-lesion nematode disease (Pratylenchus brachyurus) in potato, the objectives of this study were: a) to evaluate potato genotypes for resistance to P. infestans (Pi) and P. brachyurus (Pb); b) to investigate the fungicidal and nematicidal action of four formulations of a phytoprotective film (FP) based on chitosan and pyroligneous extract [Cu(OH) 2 +Zn+Mn; Iodine (lugol); Iodine+NaClO; garlic essential oil (OEA)] and Bordeaux syrup (BS); and c) report the occurrence of Pb in potato in the northeast. In the evaluation of late blight in the field, CIP 392.617-54 and Catucha were resistant (R) to moderately (mod) R; Cristal, BRS Pérola and F50.08.01, susceptible mod (S) to R; BRS Clara and Markies, S to mod R; and, the other genotypes (Camila, F63.10.07, F05.11.03, Odone 80.02, Agata, Asterix, F21.07.09 and F183.08.01), from mod S to S. About the reaction to Pb (greenhouse conditions), Asterix, Catucha, Markies, Clara, F183.08.01, F50.08.01 and C2743.01.09 were R; and, Agata, S. From the results obtained in the reaction to Pi, 'Catucha', 'Clara' and 'F50.08.01' were selected for the subsequent experiments. In the evaluation of Pi colonization and sporulation in leaf discs on aqueous suspensions of formulations at 10, 20, 30 and 100% and CB (0.25%); the treatments at 20% was selected for the other studies. All treatments showed in vitro volatile effect on Pi mycelial growth and the greatest inhibition occurred with FP+OEA. At screen house conditions, potato plants of the selected genotypes were sprayed with the formulations at 20% and BS. From the collected potato leaves of these different treatments, the effect of formulations on the pathogen and activity of resistance-related enzymes was evaluated. Greater reductions in the Pi sev occurred with FP+Cu(OH) 2 +Zn+Mn when the inoculation occurred after treatments; and, proceeding the foliar spraying after inoculation, this reductions was noted at all formulated in 'Clara' and 'F50.08.01' cvs. There was a significant interaction between treatments and potato genotypes for enzymatic activity of peroxidase and polyphenoloxidase, whose increase or decrease varied according to the factors; and, variation in total protein content was verified with BS and FP+Cu(OH) 2 +Zn+Mn regardless of the cultivar. Increase in tuber mass was observed in 'Clara' treated with FP+Cu(OH) 2 +Zn+Mn and BS, and, with FP+Iodine in ‘Catucha’ and ‘F50.08.01’. The root-lesion nematode Pb was identified in tubers of potato 'Agata' from Mucugê-BA; and the inoculated plants showed a reduction in the fresh mass of roots and shoots besides an anticipation of its cycle. In vitro nematicidal effect of FP 20% and BS formulations was observed on Pb specimes; and, the spraying of these formulations in the soil with subsequent planting of sorghum at greenhouse, resulted in the nematode suppression at all treatments as well as an increase in root fresh mass with FP+(Cu(OH) 2 +Zn+Mn) was also observed.