Almond Hull-Split Model Development

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Typically, warm springs accelerate fruit development. The period from full bloom (FB) to fruit maturity for individual cultivars of peach, nectarine, plum, and prune is influenced by daily temperatures between the start of FB and 30 days after FB (DAFB) (Marra et al., 2002). As with these related species, early fruit development in almond is also quite sensitive to spring air temperature.

In almond, the date of “hull-split” (HS) signals the beginning of fruit maturity. A goal of the 8-year study was to examine the correlation between the length of the period between FB and HS in almond and temperature accumulation after the start of FB, and thus, base the model on the collection and analysis of this type of data.

Data analyses indicated that the length of the period from FB to HS was negatively correlated with the accumulation of Growing Degree Days between FB and 90 DAFB (GDD90). Calculations of GDD90 were based on the single sine method (Zalom et al., 1983). Results of the 8-year study indicate that temperatures in the first 90 DAFB are a primary factor influencing the time of nut maturity in almond cultivars in California. This is in contrast to previous studies with peach, nectarine and plum, which indicated a strong relationship between fruit development and Growing Degree Hours in the first 30 days after full bloom (GDH30) (Ben Mimoun and DeJong, 1999; DeBuse, et al., in press).

Data on 28 California almond cultivars were evaluated in the study, but the predictive model is currently applicable to these 12 important cultivars: 'Nonpareil', 'Sonora', 'Price', 'Ruby', 'Wood Colony', 'Padre', 'Butte', 'Aldrich', 'Winters', 'Monterey', 'Mission' and 'Carmel'. The relationship between DAFB to 1% HS and GDD90 for each of these 12 cultivars is shown in the figures below. For the full study, including regression statistics, see Tombesi, et al., 2010.

figure 1a — Figure 1a. The relationships between the number of days after full bloom (DAFB) to 1% hull-split and the accumulated Growing Degree Days between full bloom and 90 DAFB (GDD90) for six "early" almond cultivars grown at 3 orchard sites in California over 8 years.

figure 1b — Figure 1b. The relationships between the number of days after full bloom (DAFB) to 1% hull-split and the accumulated Growing Degree Days between full bloom and 90 DAFB (GDD90) for six "late" almond cultivars grown at 3 orchard sites in California over 8 years.