DIAGNOSIS OF BORON STATUS IN AVOCADO TREES (PERSEA AMERICANA MILL.) USING ALTERNATIVE TISSUES

A tissue analysis trial for the diagnosis of boron (B) status was performed during the 2003 growing season in Paine County, Metropolitan Region, Chile (lat. 33º44’ S, long. 70º39’ W). Five-year-old ‘Hass’ avocado (Persea americana Mill.) trees treated with borax applied to the soil surface at rates of 0, 75, 150 or 300 g tree-1, each with three replicates. Borax was incorporated into the soil applying half of the dose on each side of the tree along the closest irrigation furrow. Borax was applied on January 29th, approximately three months after bloom. Thirty spring flush leaves per tree were collected on May 22nd and October 10th, four and 10 months after borax application. Sixty inflorescences per tree were collected on October 10th, just before flower anthesis. Boron concentration in leaf and inflorescence was determined by spectrocolorimetry (Azomethine H). Boron concentration was higher in the inflorescence, followed by the May leaf sample. Boron concentration in the inflorescence and October leaf sample increased directly with borax rate. In contrast, B concentration in the May leaf sample, only increased at the highest rate of applied borax. Regression analysis between B rate and B concentration of inflorescence and leaf tissue in October indicated a higher R² coefficient (0.82 and 0.78 respectively) than the May leaf sample (R² = 0.63). The results of this study suggest that inflorescence can be used to diagnose the B status of avocado trees more accurately than the current standard May leaf sample.