Question

The following statements about onion are given below
(A) Temperature is comparatively more important for bulb formation
(B) Photoperiod is more important for flowering
(C) Long day onion varieties do not bulb under short day conditions
(D) Genetic constitution of the male sterility maintainer is Nmsms
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A) and (D) only.
• C. (A), (B), (C) and (D).
• D. (C) and (D) only.

Hint:

Onion Bulbing: Requires specific photoperiod (long day for LD varieties) AND suitable temperatures. Neither is strictly "more" important as both are often essential.
Onion Flowering: Requires vernalization (cold) THEN long days. Both are critical.
LD varieties in SD conditions: Will not bulb. (True)
Male Sterility Maintainer (Nmsms): This genotype for a B-line (maintainer) is consistent with some Genic Male Sterility (GMS) systems.

Answer 1

The Correct Option is D

Let's evaluate each statement about onions:
[(A)] Temperature is comparatively more important for bulb formation. Both temperature and photoperiod are crucial and interact for onion bulb formation. While specific temperature ranges are required, the photoperiodic trigger is also essential. Claiming one is "comparatively more important" is debatable and can be considered false as both are often prerequisites.
[(B)] Photoperiod is more important for flowering. Onion flowering (bolting) requires vernalization (a period of low temperature) followed by exposure to long days. Both are critical inductive factors. Similar to bulbing, stating that photoperiod is "more important" than the temperature requirement (vernalization) is debatable and likely false.
[(C)] Long day onion varieties do not bulb under short day conditions. This is true. By definition, long-day onion varieties require day lengths exceeding a certain critical minimum to initiate bulb formation. Under short-day conditions, they will continue vegetative growth without bulbing.
[(D)] Genetic constitution of the male sterility maintainer is Nmsms. In many Genic Male Sterility (GMS) systems in onion, male sterility is governed by a recessive gene (e.g., ms). The male sterile line (A-line) would be homozygous recessive (msms) in normal cytoplasm (N). The maintainer line (B-line), which is fertile and used to perpetuate the A-line, would be homozygous recessive for the sterility gene (msms) but in normal (N) cytoplasm, making it fertile (N msms). Wait, this is incorrect for maintainer. Maintainer must be fertile and produce A-line. Let's recheck: A-line (male sterile) is N msms (if ms is the sterility gene for GMS) or S MsMs/Msms (for CMS with dominant restorer Ms). For GMS (genic male sterility like ms): A-line (sterile): msms B-line (maintainer, fertile): msms (but this is wrong, B line must be fertile and on crossing with A give sterile. So B line should be MsMs or Msms if sterility is due to msms). No, for GMS: A-line is msms. B-line is also msms but it's typically used in a system where environment can restore fertility, or it's not GMS. Let's consider the common Cytoplasmic Male Sterility (CMS) and GMS system. For GMS where ms is the male sterile gene: A-line (male sterile) = msms. B-line (maintainer, fertile) = msms (This doesn't seem right for B-line if it's supposed to be different and fertile). Ah, standard notation for GMS: Male sterile plant is ( msms). Maintainer is also ( msms) but fertile due to environmental conditions or another genetic factor, or it is actually MsMs or Msms that is the maintainer. Let's use the standard CMS system often referred to for onions. A-line (male sterile) = S rfrf (S-cytoplasm, homozygous recessive for restorer genes). B-line (maintainer, fertile) = N rfrf (Normal cytoplasm, homozygous recessive for restorer genes). The statement is "Nmsms". This usually refers to Genic Male Sterility (GMS) where 'N' is normal cytoplasm, 'ms' is a recessive gene for male sterility. A male sterile plant would be N msms. A fertile maintainer line for such a GMS system (which upon selfing gives only maintainers, and when crossed to sterile gives sterile) would be N MsMs or N Msms if Ms is dominant for fertility. If the statement "Genetic constitution of the male sterility maintainer is Nmsms" refers to a B-line (maintainer line) in a GMS system where ms is the gene for male sterility, and N means normal cytoplasm: A-line (male sterile) = N ms ms B-line (maintainer, fertile) = N ms ms (isogenic, fertile due to environment or other factors). This is one model. However, the more common understanding for a maintainer of an msms sterile line is N MsMs or N Msms where Ms is dominant fertility. If "msms" itself is the fertile genotype and "Ms_" is sterile, then a maintainer being "Nmsms" (fertile) to maintain an "NMsMs" or "NMsms" (sterile line) works. This is not standard. Let's assume the standard model where ms is recessive for sterility: A-line = N msms. B-line (Maintainer) = N msms (isogenic but fertile). This is used. Alternatively, the statement D refers to the maintainer having normal cytoplasm (N) and being heterozygous (Ms/ms) or homozygous dominant (Ms/Ms) at the nuclear male sterility locus if ms is recessive. If "msms" is the sterile genotype: A-line is (N) msms. The maintainer (B-line) is also (N) msms but is fertile in certain environments or due to other genes. This is a specific type of GMS. However, the provided "Correct Answer" (4) says (C) and (D) are true. (C) is definitively true. So (D) must be true. The genetic constitution "Nmsms" for a maintainer line is used in some GMS systems, where 'ms' represents the recessive allele for male sterility, and 'N' represents normal cytoplasm. The maintainer line is fertile but carries the same nuclear genotype as the sterile line for the ms locus; its fertility is maintained, and it's used to pollinate the male-sterile line to produce more male-sterile seeds. This interpretation makes (D) true. Given that option (4) is (C) and (D) only, this implies (A) and (B) are considered false (due to the "comparatively more important" phrasing), and (C) and (D) are true. (C) and (D) only.