Question

Adventive embryony in Citrus is due to
A. Nucellus
B. Integuments
C. Zygotic embryo
D. Fertilized egg

Answer 1

A diploid cell directly generates an embryo without fertilization. There is no sexual contact or meiosis in this process. The cells surrounding the ovule tend to perform embryogenesis depending on their abilities.

Complete solution:
Citrus is a flowering plant. Plants in this genus form citrus fruits like oranges, lemons etc. They belong to the Rutaceae family.
Firstly, we should learn what is adventive embryony? When the reproductive cells are not responsible for the embryo formation and it is formed without fertilization. This process is called adventive embryony.

Let us see which out of the four options can perform adventive embryony.

Option A – Nucellus: It is a tissue in the ovule surrounding the embryo. Mostly nucellus provides nourishment to the embryo but sometimes it starts to produce embryos genetically identical to the parent plant. This mechanism is called adventive embryony or nucellar embryony. It occurs in crassinucleate ovules, example- citrus.
Option B – Integuments: Integument is the protective tissue around the ovule. These get converted into seed coats after maturation of the ovule. Integumentary embryony occurs in uninucleate ovules, example- euonymus.
Option C – Zygotic embryo: When a zygote undergoes a series of differentiation giving a mature embryo, it is called a zygotic embryo. It occurs in higher plants. In this a male gamete fertilizes the female gamete to produce zygote and ultimately the embryo.
Option D – Fertilized egg: A fertilized egg is caused by fertilization which is contradictory to the definition itself. In the definition, we learnt that in adventive embryony fertilization does not occur.

So the answer is option A: Nucellus

Note: Diploid sporophytic cells form the embryo without involving any meiosis or sexual contact. A seed in citrus has one normal embryo and many adventives embryos. These embryos develop from the somatic cells of the nucellus.