Loss of kernel quality associated with harvest delays in Tasmania, Australia

The Australian walnut industry is undergoing rapid expansion with the potential to supply high quality nuts to local and export markets. Optimizing the quality of nuts is essential to maximise these opportunities. However, knowledge of the factors that adversely affect nut quality in Tasmania, Australia, is limited. Thus, trials over two years investigated the temporal development of fruit maturity and the effect of harvest delays on nut quality. The progression of kernel maturity, or packing tissue brown (PTB), was similar in Lara, Vina, Howard and Chandler, with 95% PTB predicted between 77 and 85 days after 1st January. The onset of harvest, defined as 80% hullable fruits, was also similar for the four cultivars, occurring within a 6 day period. The predicted PTB in Serr was at least 18 days sooner than other cultivars. Delaying harvest of mature nuts significantly reduced kernel quality in both years. In 2010, delaying harvest reduced the incidence of Chandler, Howard and Vina nuts with extra-light kernels i.e., between 57 and 63% of Chandler nuts had extra-light kernels if harvest was delayed by 7 days or more, whereas 77% of nuts had extra-light kernels if harvest was not delayed. Delaying harvest by 7 days significantly increased the incidence of nuts with yellow pellicles i.e., from less than 6% of nuts if harvest was not delayed to 24, 28 and 51% of Howard, Vina and Chandler nuts, respectively, if harvest was delayed. Similarly, in 2012 Lara and Chandler nuts harvested 8 days or more after shaking had fewer extra-light kernels, and more yellow pellicle and moulds, compared to nuts harvested earlier. Further research will identify seasonal variations and improve this initial description of temporal fruit maturity and factors affecting nut quality.