Double kerneled fruits in almond (Prunus dulcis Mill.) as related to pre‐blossom temperatures

Summary A ten year study on the influence of pre‐blossom temperatures on the percentage of double kerneled almond fruits, under warm climatic conditions, showed a negative correlation between the percentage of fruits with double kernels and mean temperatures during the pre‐blossom months. When mean temperatures for single pre‐blossom months were correlated with double‐kernel production, mean temperatures in December showed a much larger correlation (r = ‐0.78) than those of November (r = ‐0.51) or January (r = ‐0.31). Artificially induced 3–4°C daytime increases in pre‐blossom temperature on the variety ‘Malagueña’ which commonly produces double kernels, caused a marked fall in the percentage of double kerneled fruits, although it did not affect the percentage fruit set. Our results may indicate an important influence of pre‐ blossom temperatures on ovule viability.