A Prospective Study to Determine Causes of Physiological Disorder in ‘Chandler’ Walnut Fruits.

In the last 10 years Chilean walnut production has become an important economical activity. The industry considers internal and external features of the nut to determine its quality and price; some of the defects considered for discard are: open or imperfect shell, cracked or broken walnut, adhered hull presence and split walnut among other alterations. In ‘Chandler’ walnut fruit, a physiological disorder occurs that is only perceptible at harvest; that disorder is observed as a disruption of the endocarp structure, with high presence of perforations. Among other factors, fruit mineral content have shown an important role in determining fruit quality in different species. In the present study we made a prospection of the mineral composition of fruits, comparing element concentrations from nuts with and without symptoms of endocarp disruption. The study was carried out in a ‘Chandler’ walnut commercial orchard located in a central area of Chile. To characterize the soil, a representative sample was taken to analyse parameters such as pH, macro and micro nutrient supply. Soil fertility didn´t show deficiencies of any of the measured nutrients. At harvest, a fruit sample was taken, and then classified into groups according to visual symptoms: severe, moderated, and none endocarp disruption presence. Later, a group of 10 fruit from each level was craked in order to split the nut into shell (nut endocarp) and seed. Dry matter and mineral concentration of nutrients were measured from each disorder level and tissue. The mineral elements measured were: N, K, Ca, Mg, Mn, Zn, Cu, Fe and B. Shells with severe disorder symptoms had higher N, Zn and Cu concentration, and K/Mg ratio, compared with shells with moderated symptoms, and at the same time, the endocarp with moderated symptoms had higher levels compared with shells without the disorder. Shells and seeds without disorder showed higher Ca concentrations, lower N/Ca, K/Ca and Zn/Mn ratios, compared with shells and seeds with moderated and severe symptoms. According to these results the observed disorder of the nut endocarp in ‘Chandler’ cultivar has a close relationship with an unbalanced mineral composition of the fruit.