Influence of Bioregulators on Latex Yield and Proteolytic Activity of Papain Extracted from Field-grown TNAU Papaya CO. 8 under the Natural Incidence of Papaya Ring Spot Virus

Abstract

The cultivation of papaya for both fruits and commercial papain extraction drastically suffers often due to the devastating incidence of papaya ringspot virus disease. The present study aimed to find out whether the papain yield and quality are influenced when bioregulators are applied to manage papaya ring spot virus (PRSV) incidence or as a measure to limit the height of the crop in TNAU Papaya CO.8 variety grown in the open field with the natural incidence of PRSV. Three growth retardants [250 ppm of prohexadione calcium (G2), 500 ppm of mepiquat chloride (G3) and 500 ppm of chlormequat chloride (G4)] and three stress tolerance promoting bioregulators [100 ppm of methyl jasmonate (S2), 100 ppm of salicylic acid (S3) and 0.6 g/ l of strobilurins (S4)] were employed in the study. Water spray (G1 and S1) was kept as control. The treatments were imposed at 4th and 8th months after planting. The growth retardants were initially sprayed and, in the subsequentweek ,the stress tolerance promoting bioregulators were sprayed as per the recommended doses. Among the combinations tried, spraying 250 ppm of prohexadione calcium followed by water spray (G2S1) a week later recorded the lowest plant height (140.79 cm) at the time of fruiting. The treatment combination G 2S2 involving 250 ppm of prohexadione calcium and 100 ppm of methyl jasmonate registered a higher number of fruits (42.17). The combination of 250 ppm of prohexadione calcium along with 100 ppm of salicylic acid (G2S3) was found to be the most effective combination to manage PRSV without compromising papain production and to enhance the proteolytic activity significantly (44378.36 TU g-1) as compared to other combinations. The treatment combination of 500 ppm of mepiquat chloride and 100 ppm of salicylic acid (G3S3) favored higher dry latex yield apart from a significant reduction in PRSV symptoms. Both these treatment combinations (G2S3 and G 3S3) merit due consideration in PRSV management for commercial fruit and papain production in papaya