Rootstock Affects Yield, Yield Efficiency, and Harvest Rate of 'Kensington Pride' Mango

Low yields and high harvesting costs are long-standing problems in mango (Mangifera indica L.) cultivation. In an ef fort to increase productivity in the scion 'Kens- ington Prideʼ we examined the im pact of nine different rootstocks over a 10-year period. Rootstock effects on fruit pro duc tion were signifi cant in most seasons, and cu mu la tive yields (nine seasons of crop ping) for the best treatment ('Sg. Siputʼ) exceeded those of the poorest treatment ('Sabreʼ) by 141%. Yield effi ciencies (ex pressed on both a trunk cross-sectional area and canopy silhouette area ba sis) were also signifi cantly affected by root stock. Root stock effects on yield and yield effi ciency were generally consistent across seasons, despite large seasonal variations in yield. Harvest rates were also infl uenced by root stock, and were poorly correlated with tree size. These results demonstrate pos si bil i ties for manipulating mango scion pro duc tiv i ty through rootstock gen o type. followed by a distinct dry period for most of the remaining months. Orchard management followed standard com mer cial practices, as described in Crane et al. (1997). Pruning was restricted to establishing a strong framework of branches, preventing fruit developing on the ground (skirting), and enabling spray pen- e tra tion of the canopy (light internal branch thinning). The soil type was a Venn sandy loam (sandy, Typic Alfi sol). Ground-water, used for irrigation, contains calcium bi car bon ate which causes an increase in soil pH to between 8 to 8.5, while electrical conductivity remains low (<0.05 dS·m -1 ). Trees were arranged in a randomized com plete-block design with six single tree rep li ca tions of each of the nine rootstock treatments. Trees were spaced at 5 m within the row and 13.5 m between rows. Whole tree yields were measured for 1987 through 1996, (ex clud ing 1991). Harvest date was determined by testing internal fruit maturity and normally occurred in early November of each season. The com plete absence of rain for at least 3 months prior to fl owering, coinciding with the onset of cooler night temperatures, produced syn chro nous fl owering in each year of the ex- periment. This in turn resulted in uniform fruit maturity and enabled all fruit to be re moved in a single harvest (which is the stan dard commercial practice in most seasons in this production region). Fruit number, weight, and tree harvest time (harvest rate) were re cord ed for each tree in the experiment. Tree size was determined using two meth- ods and these measurements were then used to calculate yield effi ciencies. One of these meth ods expressed tree size in terms of the area of the projected canopy silhouette of each tree ("canopy silhouette area" (CSA)), while the other method expressed tree size in terms of the dimensions of the trunk ("trunk cross-sec tion al area" (TCA)). CSA was mea- sured in 1991, 1993, and 1996 using methods similar to those described in Richards (1992). Pho to graphs were taken from each side of each tree and scanned into image processing software (SigmaScan; SPSS, Chicago). The tree outline on each image was traced and the number of pixels within the traced area com put ed. A marker board (of known area) held at the edge of the tree canopy on each image was then traced and used to scale each mea sure ment. Trunk circumference was measured slight ly below the graft union, ≈200 mm above ground level. These measurements were made each season from 1990 to 1996 (ex clud ing 1991 and 1993), and used to cal cu late TCA. Data analysis was performed using anal y sis of vari ance and correlation pro ce dures with in GENSTAT (Genstat 5; Lawes Ag ri cul tur al Trust, Rothamsted, England).