Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
A number of pea fields have had cold injury this year. One issue that could be a concern is early pea fields with reduced seed set. This is where pods develop but only one or two seeds are formed.
Reduced seed set in peas.
Reduced seed set occurs during flower development and pollination. Peas are self-pollinated. As the flower opens, the pollen from the anthers is released to the stigma of the pistil of the same flower. Once on the pollen is on the stigma, the pollen germinates and a pollen tube is formed and then grows down the style and when it reaches the ovule, the egg is fertilized by one of the two sperm cells, the other fuses with polar nuclei to become the seed endosperm. During the development of the pollen tube, plant hormones are released which are also essential for seed set.
Seed set problems therefore may be related to lack of pollen formation, pollen that does not release to the stigma, reduced pollen germination, abnormal pollen tube development, abnormalities in the stigma or stile, or abnormalities in the ovule. Lack of Gibberellin hormone release has also been shown to reduce seed set or lead to early seed abortion in peas.
What are the potential causes of reduced seed set in peas? Frost or freeze when flowers are opening has the potential to injure pollen or directly damage flower parts. Peas are very cold tolerant normally but are susceptible to injury at flowering. There was a frost on much of Delmarva on April 29 and 30 where temperatures dropped to the mid to upper 20’s. Cold stress to peas at and after flowering has been shown to cause seed abortions in some varieties (several days below freezing in a row).
Other research has shown that peas under temperature and moisture stress produce fewer seeds. Experiments have shown that temperatures at 93°F or above can also reduce seed set in some varieties of peas. Dry soil conditions will magnify this effect.
Another factor to consider is timing of chemical applications to peas – applications near and at flowering may damage pea flowers under certain weather conditions and reduce seed set.