EFFECT OF PYRACLOSTROBIN ON TOMATO CROP UNDER SALINITY STRESS

Tomato for processing is a very widespread crop in the Mediterranean area where often there are problems of high salinity of irrigation water. It's well known that the high salinity creates physiological problems with considerable negative effects on production. Pyraclostrobin belongs to a class of fungicide (strobilurins) having a broad spectrum of applications, with preventive, curative, translaminar and locosystemic properties. In the literature it is reported that strobilurins can affect the plant metabolism resulting in the increase of yield, dry matter, content of both chlorophyll and protein and delay senescence. In addition, it was observed plant water balance modification by reducing root water uptake, resulting in the postponement of soil dehydration, so it may contribute to yield enhancement. Because many effects of salt stress are comparable to water stress, we may speculate that Pyraclostrobin could alleviate detrimental effects of salinity on plants. This study focused on the interactive effect of salinity and Pyraclostrobin application on tomato grown in pots under plastic tunnel. The objective was to investigate the complementary properties of Pyraclostrobin in the improvement of tomato physiological (SPAD, gas exchange, activity of antioxidative enzymes as SOD, CAT, POD, APX), yield and fruit quality responses under salinity. A two-year research (2010 and 2011) was carried out in Basilicata region, southern Italy, on cv Coronel to compare two soil salinity levels - 1.0 (S0) and 5.4 dS m-1 (S1) - and two fungicide treatments - application of fungicides without strobilurins (F0); application of a strobilurin based fungicide (Cabrio® Duo) (F1). The treatments were arranged in a split plot design with seven replicates. On overall, when plants are treated with Pyraclostrobin, a considerable increase in POD, APX and CAT activity occurred, whereas no significant changes were observed in SOD. Different extent of changes in enzyme activity was observed in the two parts of the plant: POD increased only in roots, APX in roots as well as in leaves, and CAT only in leaves. In some sampling date, the increase in antioxidant enzyme activities was higher in saline stressed plants. The amount of chlorophyll, measured in SPAD units, did not differed between salinity levels, instead, F1 showed the increase of about 6%. Gas exchanges were influenced by salinity level and fungicide treatments. In particular, S1 has shown values of net assimilation (A), transpiration (T) and stomatal conductance (gs) respectively of about 17, 26 and 22% lower than S0, while the water use efficiency (WUE) was not influenced. Pyraclostrobin reduced A and T by about 8%, and gs by about 17%. Salinity reduced fruit mean weight by 19%, total and marketable yield by 25 and 21%, respectively, and increased fruit blossom-end rot (BER) by 57%. Among the qualitative parameters, salinity caused the increase of total soluble solids (TSS) and dry matter (DM) of the fruits by 22 and 20% respectively. Pyraclostrobin increased fruits mean weight by 6%, total and marketable yield by about 8% and reduced BER by 19%. The improvement in total and marketable yield caused by Pyraclostrobin was higher in the crop with salinity stress (11.6%) in respect to the non saline one (6%). The reduction in A caused by Pyraclostrobin seems contradictory with the yield increase, so further research is needed to study the physiological mechanisms involved when Pyraclostrobin was applied. In view of the positive effects observed with the application of Pyraclostrobin, it should be promoted its use in programs of protection of tomato crop, above all in areas with salinity problems.