Mineral Nutrition

• Ambiphotoperiodic Flowering: Ambiphotoperiodic plants flower under both short-day photoperiods ($\lt 12\text{ h}$) and long-day photoperiods ($\gt 16\text{ h}$), but remain strictly vegetative under intermediate day lengths ($12\text{ to }16\text{ h}$).
• Representative Taxon: Setaria verticillata (bristly foxtail) is the classic textbook example of an ambiphotoperiodic species.

Correct option: (1) Setaria verticillata

• Short-Day Plant Induction: Cosmos bipinnatus is a qualitative/quantitative short-day plant (SDP) whose floral transition and flower development are accelerated when the day length is shorter than its critical photoperiod.
• Comparative Taxa: Ricinus communis is day-neutral; Beta vulgaris (sugarbeet) is a long-day plant requiring vernalization.

Correct option: (3) Cosmos bipinnatus

• Two-Phase Flowering Theory: Formulated by Russian physiologist M. Kh. Chailakhyan (1958).
• Postulate: Florigen consists of two complementary physiological components acting in two sequential stages:

• Gibberellins: Required for stem elongation, bolting, and flower stalk growth.
• Anthesins: Hypothetical flowering factors required for flower bud initiation and floral organogenesis.
  
  Correct option: (1) Chailakhyan

• Assertion (A) is True: Hybrid embryo rescue (excising immature embryos and culturing them in nutrient media in vitro) is a cornerstone technique for overcoming post-zygotic barriers in wide/interspecific hybridization.
• Reason (R) is True & Explains (A): Interspecific crosses frequently trigger somatoplastic sterility, wherein the hybrid endosperm fails to develop properly and degenerates early, starving the developing hybrid embryo and causing seed abortion unless rescued in time.
• Conclusion: Both (A) and (R) are true and (R) is the correct explanation of (A).

Correct option: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)