Phenology

Developmental processes are defined in this context as the time between like and dissimilar events, or the duration of a process. Like events include the time intervals between mainstem leaves and branch leaves on a plant. Unlike events include the intervals between plant emergence and formation of a flower bud, flower or mature fruit. Duration of a process might include the period between unfolding of leaves and the time required for a leaf or internode to reach its maximum size.

Temperature and photoperiod are the two main environmental factors that determine flowering in young and established plants. Commercially grown cotton cultivars are not very sensitive to photoperiod, but are very sensitive to temperature (K.R. Reddy et al., 1997b). The effects of temperature and [CO2] were nicely illustrated (K.R. Reddy et al., 1997a) by conducting an experiment at ambient and twice-ambient atmospheric [CO2] at five temperatures. The

1995 temperature in Mississippi was used as a reference, with the other temperatures being 1995 minus 2°C, and 1995 plus 2, 5 and 7°C. Daily and seasonal variation and amplitudes were maintained. Developmental events occurred much more rapidly as temperatures increased. Number of days to the appearance of first square (flower bud), first flower and mature open boll decreased as the average temperature increased during development of the respective events (Fig. 8.8). However, the plants grown in chambers with an average daily temperature of 32.3°C did not produce any mature bolls unless there were a few cooler days immediately after flowering. The time required to produce squares, flowers and mature fruit was reduced by an average of 1.6, 3.1 and 6.9 days per degree of increased temperature, respectively. Thus,

0.07

0.06

0.05

0.04

0.03

0.02

0.01

If 0.01

15 20 25 30 35 40

Temperature (°C)

Fig. 8.8. Role of temperature on daily progress of various phenological events: (a) from cotton plant emergence to first flower bud formation (square); (b) square to flower; (c) flower to open boll. Some bolls survive average temperatures of 32°C if conditions are cooler for a few days after flowering. There were no differences between CO2 levels. (K.R. Reddy et al, 1997b.)

Emergence to square o Upland (a)

O Pima

Emergence to square o Upland (a)

O Pima

15 20 25 30 35 40

Temperature (°C)

Fig. 8.8. Role of temperature on daily progress of various phenological events: (a) from cotton plant emergence to first flower bud formation (square); (b) square to flower; (c) flower to open boll. Some bolls survive average temperatures of 32°C if conditions are cooler for a few days after flowering. There were no differences between CO2 levels. (K.R. Reddy et al, 1997b.)

assuming the temperature increase will be equally distributed throughout the growing season, a 5°C increase in average global temperature should speed development from emergence to maturity by 35 days. Unfortunately, the data suggest that most of the shortening of developmental time occurs during the boll growth period and this results in smaller bolls, lower yields and poor quality lint (Hodges et at, 1993). Doubling atmospheric [CO2] did not affect the developmental rates (Figs 8.8 and 8.9).

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment