Review of Literature: Drought and Its Effect on Okra Production
CHAPTER 2
REVIEW OF LITERATURE
2.1. Drought and its types
Okra (
Abelmoschus esculentus
L. Monech) is an important vegetable grown in
Pakistan and developing worl d and is equally favourite among the rich and poor. Due to its flower structure it is responsive to breed ing and selection, but l iterature on the genetics of drought tolerance in this ve getable is not freque ntly available. Drought is a condition in which soil moisture contents are too low or tightly attracted by soil particle (due to lower osmotic potential) so that plant cannot w ithdraw it or even if it absorbs it cannot meet its transpiration demands. There are different types of dr ought depending upon the growth stage of plant at which it occurs (Seghatoleslami, et al.
2007; Sinaki et al.
2007;
Kron et al.
2008). The stress that o ccurs at seedling stage or during development phase may be called as early drought. Such type of drought usually reduces the crop stand and as a result it damages yield due to lo wer than optimum plant population (Ashraf et al.
2005). However, farmers usually respond to this drought by replanting their crops
(Muasya and Diallo, 2001). This type of stre ss has been proved leth al for early maturing varieties (Muasya and Diallo,
2001), which seldom recover fr om the stress while late maturing varieties have enough time to recover.
Drought occurring during vege tative growth period is ca lled as vegetative phase drought. This type of drought affects plants assimilatory organs, which usually decrease in number and size resulting in lower photos ynthates production (Kaiser, 1987; Chaves,
1991; Larcher, 1995; Chaves et al.
2002). As a result yield decreases due to less amount of assimilate availabl e to the developing pods.
The third type of stress de velops during bud formation, fl owering and grain filling period. It reduces yield due to abortion of ovule, embryo and sterility of pollen. Review of previous
REVIEW OF LITERATURE
2.1. Drought and its types
Okra (
Abelmoschus esculentus
L. Monech) is an important vegetable grown in
Pakistan and developing worl d and is equally favourite among the rich and poor. Due to its flower structure it is responsive to breed ing and selection, but l iterature on the genetics of drought tolerance in this ve getable is not freque ntly available. Drought is a condition in which soil moisture contents are too low or tightly attracted by soil particle (due to lower osmotic potential) so that plant cannot w ithdraw it or even if it absorbs it cannot meet its transpiration demands. There are different types of dr ought depending upon the growth stage of plant at which it occurs (Seghatoleslami, et al.
2007; Sinaki et al.
2007;
Kron et al.
2008). The stress that o ccurs at seedling stage or during development phase may be called as early drought. Such type of drought usually reduces the crop stand and as a result it damages yield due to lo wer than optimum plant population (Ashraf et al.
2005). However, farmers usually respond to this drought by replanting their crops
(Muasya and Diallo, 2001). This type of stre ss has been proved leth al for early maturing varieties (Muasya and Diallo,
2001), which seldom recover fr om the stress while late maturing varieties have enough time to recover.
Drought occurring during vege tative growth period is ca lled as vegetative phase drought. This type of drought affects plants assimilatory organs, which usually decrease in number and size resulting in lower photos ynthates production (Kaiser, 1987; Chaves,
1991; Larcher, 1995; Chaves et al.
2002). As a result yield decreases due to less amount of assimilate availabl e to the developing pods.
The third type of stress de velops during bud formation, fl owering and grain filling period. It reduces yield due to abortion of ovule, embryo and sterility of pollen. Review of previous