In plums different pollinations can result in differences in the time of maturity and in the size of the fruit. The pollen influences the development of the fruit inasmuch as defective embryos promote earlier ripening and smaller fruits. Further, the wider the difference between the two parents, the more defective the embryos. The developmental differences in the fruit are an expression of different degrees of seed growth.
In some varieties of pears frost injury to the styles induces parthenocarpy, i.e. the complete absence of embryo development.
Difference in the fruit due to the action of the pollèn (formerly known as xenia) fall into three classes: (1) where the developing zygote is affected, (2) where the endosperm is affected, (3) where the effect is on the maternal tissues. In classes (1) and (2) the effects or differences are due to the action of paternal genes in heredity, and since they are readily explicable on a simple genetic basis there is no reason why they should continue to be referred to as xenia. In class (3) they are due to differences in the constitution and development of the embryo, endosperm and seed which affect the development of the maternal tissue. At one extreme the fruits are seedless (parthenocarpy), and at the other they have seeds larger than normal.
Volume 100, 2021
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