Question

Long Answer Question:

Describe the types of plants on the basis of photoperiod required, with the help of suitable examples.

Answer 1

Based on the photoperiodic response, plants were classified into three categories viz. Short Day Plants (SDP), Long Day Plants (LDP) and Day Neutral Plants (DNP).

1. Short Day Plants (SDP):

i. Critical photoperiod is the length of photoperiod above or below which flowering occurs. Short Day Plants usually flower during winter and late summer when day length is shorter than the critical photoperiod.

ii. These are called long night plants because they require long uninterrupted dark period/ night for flowering.

iii. If dark period is interrupted even by a flash of light, SDP will not flower.

iv. Some of the short-day plants are Dahlia, Tobacco, Chrysanthemum, Soybean (Glycine max), Cocklebur (Xanthium), cotton, etc.

2. Long Day Plants (LDP):

i. Plants that flower during summer are called long-day plants.

ii. They require a longer duration of light than the critical photoperiod, for flowering.

iii. They are called short night plants as they require a short dark period.

iv. When long dark period is interrupted by a brief flash of light, LD plants can flower e.g. pea, radish, sugar beet, cabbage, spinach, wheat, poppy, etc.

3. Day Neutral Plants (DNP):

a. These plants flower throughout the year-round, independent of the duration of light (photoperiod).

b. They do not require specific photoperiod to flower.

c. Therefore, they are called day-neutral plants e.g. Cucumber, tomato, sunflower, maize, balsam, etc.

Photoperiodism-