REPLACING SULPHUR DIOXIDE IN POSTHARVEST MANAGEMENT OF THOMPSON

REPLACING SULPHUR DIOXIDE IN POSTHARVEST MANAGEMENT OF THOMPSON SEEDLESS GRAPES BY USING HIGH-CO 2 CONTROLLED ATMOSPHERE Manriquez, D. 1. , Arias, M. 3, Defilippi, B. 1, 2 and Retamales, J. 1, 3 (1)Instituto de Investigaciones Agropecuarias, P. O. Box 439/3, Santiago, Chile (2)Presently at Pomology Dept. UC-Davis (3)Facultad de Ciencias Agronómicas, Universidad de Chile ABSTRACT Research work has been conducted in the past two seasons in Thompson Seedlees grapes in Chile aiming at completely replacing presently-used SO 2 fumigation and/or inclusion of metabisulphite pads during storage/transport for export. SO 2 usage prevents rotting, mainly the one caused by Botrytis cinerea which is prevalent under such circumstances. However, possible development of organic table grapes, together with expected restrictions in some markets, precludes the use of SO 2 during postharvest. An alternative to SO 2 is being presently sought by replacing it with controlled atmosphere (CA) and several combinations of CO 2/O 2 have been assayed. Fruit were inoculated with Botrytis in order to have increased propensity towards the rotting problem and were kept for periods between 20 -40 days in containers inside a cold chamber to simulate export conditions. Containers were submitted to CA conditions by attaining given gas combinations and compensating for changes caused by respiration with an automated system (Kronenberger Systemtechnik, Germany). Results show that by using elevated CO 2 levels, i. e. between 1520%, an adequate control of rotting, comparable to the one attained with the use of SO 2, can be achieved. Stalks and pedicels were less green when using CA instead of SO 2 and work is being conducted to overcome such quality problem. Table 2. Rotting incidence and rachis appearance in Thompson Seedless grapes after 20 days at 0ºC. Season 1999 -2000. Table 3. Rotting incidence and rachis appearance in Thompson Seedless grapes after 40 days at 0ºC. Season 1999 -2000. INTRODUCTION Increased interest in organic fruit, mainly in markets of developed countries, has prompted to organic cultivation of fruit crops. Table grapes are the leading horticultural crop in Chile and the country is one of the largest exporter of this fruit in the world. Infection with grey mold caused by Botrytis cinerea is the main factor limiting storage/shipment of Chilean table grapes and SO 2 is used to control it during postharvest. However, use of SO 2 is not permitted for organic produce and, thus, alternative treatments should be developed for export. Limited research has been conducted using controlled atmospheres (CA) in table grapes and no research has been performed in Chile. Thompson Seedless grapes tolerate high CO 2 (Ahumada et al. , 1996; Mitcham et al. , 1997) and control of Botrytis rot resulted from high CO 2 levels (Berry and Aked, 1997), showing a potential for CA to replace SO 2 for controlling decay in table grapes. Quality problems caused by excessive SO 2, like bleaching and hairline, and possible allergic reactions to SO 2 residues on the fruit (Berry and Aked, 1997), can determine that the replacement of SO 2 in the postharvest handling of table grapes is not only important for organic fruit, but also for conventionally-grown produce. MATERIALS AND METHODS ·Thompson Seedless grapes from organic cultivation were used in the 1999/2000 season. Grapes from conventional cultivation were used in the 2000/2001 season ·Grapes were handled as in normal procedure for export and packed in 5 kg boxes ·One berry per bunch was inoculated with a culture of Botrytis cinerea (10, 000 conidia per m. L) isolated from grapes (Picture 1) ·CA treatments (Table 1) were established by using microchambers connected to an automated system (Kronenberger Systemtechnik, Germany). ·Evaluations were performed after cold storage and again after 4 days shelf life at 18 -20ºC: - Soluble solids and total titratable acidity were measured on grape samples - Water loss by weighing individual bunches - Rachis appearance was rated from 1=green to 4=brown - Botrytis incidence was evaluated by detaching and weighing affected grapes and expressing it as percentage ·Results were submitted to ANOVA and Duncan`s test for mean separation Table 1. Description of the treatments used in Thompson Seedless grapes. Season 1999 -2000 Picture 1. CA-treated grapes after 40 days at 0ºC. Berry inoculated with Botrytis (red dot within the circle) not showing decay. Effects of high CO 2 (35%) on rachis browning are also apparent. Season 1999 -2000 Figure 2. Thompson Seedless bunches after 40 days cold storage and 8 days shelf life. The standard treatment with SO 2 -pad (left) show a decay control similar to CA treatment (right) having 15% CO 2 and high O 2. Exclusion of SO 2 -pad without CA (center) results in extremely high decay. Season 2000 -2001 CONCLUSIONS Controlled atmosphere with high CO 2 levels is able to effectively control decay caused by Botrytis cinerea in Thompson Seedless grapes and can constitute a basis for replacing SO 2 treatments in conventional and organic fruit. RESULTS There were no consistent differences in soluble solids and total titratable acidity as a consequence of the treatments (data not shown). Decay: After only 20 days at 0ºC treatments in air showed more rotting incidence and, as expected, being the treatment without SO 2 -pad the most affected one (Table 2). After 40 days at 0ºC a similar situation of Botrytis incidence can be determined (Table 3) with the CA treatments showing a decay control at least as good as the standard treatment with SO 2 -pad. As expected, after shelf life there is a marked increase in decay and the air treatment without SO 2 -pad is completely affected (Table 4). Rachis appearance: After 20 days cold storage CA treatments without SO 2 -pad resulted in poorer rachis appearance than the treatments having SO 2 -pad (Table 2). After 40 days cold storage there is an increase in the problem of browning of the rachis in the CA treatments, apparently related with increasing CO 2 levels (Table 3), getting worse with shelf life (data not shown). Interestingly, there is indication that high O 2 levels like in T 8 (15%O 2) are less detrimental than low levels in the analogous treatment (T 6=5%O 2). Apparently, thus, there is a potential of high CO 2 CA treatments in controlling decay in Thompson Seedless table grapes, with low O 2 not being required for such an effect. The problem of rachis appearance, though, is an important detrimental factor which should be solved before recommendations can be given. Therefore in the 2000 -2001 season CA treatments with high O 2 were assayed and excessive CO 2 levels were avoided. Results in the 2000 -2001 season confirm findings of the first season (Picture 2) and agree with previous research where control of germination of B. cinerea in vitro was achieved with CO 2 concentrations of 16% and higher in the presence of high O 2 (Wells and Uota, 1970). Similarly, Berry and Aked (1997) controlled Botrytis rot in Thompson Seedless with CO 2 concentrations higher than 15%. CA is less effective than SO 2 to prevent rachis discoloration, with extremely high CO 2 levels causing damages to the rachis. Low O 2 levels combined with high CO 2 apparently result in poorer rachis appearance than higher O 2. REFERENCES Ahumada, M. , Mitcham, E. and Moore, D. , 1996. Postharvest quality of Thompson Seedless grapes after insecticidal controlled-atmosphere treatments. Hort. Science 31 (5): 933 -836. Berry, G. and Aked, J. , 1997. Controlled atmosphere to the post-harvest use of sulphur dioxide to inhibit the development of Botrytis cinerea in table grapes. Proceedings 7 th International Controlled Atmosphere Research Conference. UC Davis Postharv. Hortic. Series N° 17 Vol. 3: 160164. Mitcham, E. J, Zhou, S. and Bikoba, V. , 1997. Controlled atmospheres for quarantine control of three pests of table grape. J. Economic Entomology 90: 1360 -1370. Wells, J. M. and Uota, M. , 1970. Germination and growth of five fungi in low-oxygen and highcarbon dioxide atmospheres. Phytopathology 60: 50 -53. ACKNOWLEDGEMENTS This work has been conducted within a FONTEC project with Subsole Export (M. Silva). Thanks are given to Rosita Aviles for input in management and to Marisol Pérez and Paula Castillo for valuable technical support.