Abnormal development of pollen and embryo sacs contributes to poor fruit set in walnut (Juglans hopeiensis)

Abstract

SummaryThe nuts of Juglans hopeiensis Hu are favoured by consumers for their hard shells, texture, and ornamental value. However, low rates of fruit set (5% – 20%) restrict expansion of the walnut industry in its native China. We compared the development of pistillate and staminate flowers of J. hopeiensis (‘M1’ and ‘M59’) with those of J. regia (English walnut; ‘Liaoning 1’ and ‘Lvbo’) and J. mandshurica (Manchurian walnut; ‘Qiuzi 1-17’). The latter two species generally have a high rate of fruit set (approx. 60 – 70%). J. hopeiensis pollen is dysplastic, irregular in shape, and some pollen grains are empty, whereas pollen in all other species is sub-globose when mature, and the pollen grains are generally full. The embryo sac eventually disappeared in J. hopeiensis, whereas it was well-developed in all other species. These results suggest that abnormal development of pollen and embryo sacs contributes to the low rate of fruit set in J. hopeiensis.