Water is one of the most essential components for plant organisms. It serves as a solvent of different solutes and transporter of solutes between cells and organs. The greater part of water uptake from the soil is consumed by transpiration preventing temperature increases. The rate of transpiration is directly related to the gradient of water vapour concentration in the intercellular spaces of the leaf and the ambient air. Rapid changes in the transpiration rate from a leaf or leafy shoot as a result of excision of the leaf or shoot have been observed in many plants including banana plants (Anderson et al., 1994). Rufelt (1963) stated that the increased water supply to the leaf is presumably responsible for increased stomatal opening and increased transpiration in banana, which is called “Rufelt’s hypothesis”. Allerup (1960) reported that increased stomatal opening as a result of excision of young barley leaves considers this as for Rufelt’s hypothesis. High rate of transpiration was recorded even when the stomata were apparently partially closed in banana (Shmueli, 1953). A positive correlation between relative water content and gas exchange activities was reported by David (2002) and the reduction of RWC strongly reduced photosynthesis and transpiration. Therefore, plant growth and development severely depends on water availability (Turner, 1990) and it is the primary limiting factor for banana plant growth in terrestrial ecosystems. Wilting of mesophyll cells and withdrawal of water from the epidermal and subsidiary cells permitted the guard cells to bulge outward causing opening of the stomatal pores. Decreased water supply caused the mesophyll cells to wilt. A strong stomatal opening response was observed under conditions of low transpiration. Under such conditions there would have been very little tension to relieve. Increased stomatal opening also occurred as a result of freezing rather than cutting the vascular supply to the leaf (Rufelt, 1963). Shmueli (1953) dealing with the concept of stomata and transpiration stated that stomatal closure was a major cause for decline in transpiration rate during water stress. Understanding banana plant response to soil moisture deficit and expression of leaf temperature, transpiration rate ans stomatal diffusive resistance traits are of basic scientific interest and have potential application bananas (Musa spp). With a view to elicit information on these aspects, field and laboratory investigations were undertaken. M₁ maintained the temperature around 30°C to 33°C, whereas M₂ recorded an elevated temperature of 30 to 36°C during the growth period. Among the subplot treatments, S₁₁ and S₁₂ recorded the highest temperature of about 35.3°C, whereas S₁ recorded the lowest temperature of 32.6°C. All the other subplot treatments maintained the temperature of around 34°C. Interaction effects of M at S and S at M revealed significant difference at all the stages of growth. Leaf temperature had positive correlation with yield were noticed in this present research study.

Leaf temperature was significantly influenced by both main plot and subplot treatments over the entire period of growth (Table 1; Figure 1). The main plot treatment M₁ maintained the temperature around 30°C to 33°C, whereas M₂ recorded an elevated temperature of 30 to 36°C during the growth period. Among the subplot treatments, S₁₁ and S₁₂ recorded the highest temperature of about 35.3°C, whereas S₁ recorded the lowest temperature of 32.6°C. All the other subplot treatments maintained the temperature of around 34°C. Interaction effects of M at S and S at M revealed supporting evidence significant difference at all the stages of growth. Leaf temperature had positive correlation with yield were noticed in this present research study.

Table 1 Effect of water stress on leaf temperature (˚C) at different growth stages of banana cultivars and hybrids

Figure 1 Correlation of leaf temperature and yield in banana cultivars and hybrids

The time trend of transpiration rate revealed a decreasing trend throughout the growth period of the crop (Table 2; Figure 2). Between the two main plot treatments, M₁ (86.3, 82.4, 77.7, 74.7 and 72.5 µg H₂O cm^-2 s^-1) registered significantly high rate of transpiration over M₂ (80.5, 76.6, 71.9, 69.0 and 67.0 µg H₂O cm^-2 s^-1) at 3^rd, 5^th, 7^th, 9^th and at harvest stages. Among the sub-plot treatments, S1 registered higher rate of transpiration (94.5, 88.5, 84.6, 80.9 and 76.0 µg H₂O cm^-2 s^-1) at all the growth stages, which was followed by S₂, S₃ and S₄. The significantly lower transpiration rate was, however registered by S11 and S₁₂ (62.4 and 63.6 µg H₂O cm^-2 s^-1) at 7th MAP. Interaction effects of M at S and S at M were signi- ficant at all growth stages. In this present research study, transpiration rate had positive correlation with yield.

Table 2 Effect of water stress on transpiration rate (µg H2O cm-2 s-1) at different growth stages of banana cultivars and hybrids

Figure 2 Correlation of transpiration rate and yield inbanana cultivars and hybrids

Stomatal Diffusive Resistance

Stomatal Diffusive Resistance (SDR) showed an progressive increasing trend from 3^rd to 7­th MAP stage with a sharp decline thereafter. There existed significant differences in main and sub plot treatments at all stages (Table 3). Comparison of two treatment at main plot level revealed that, M₂ had higher SDR of 0.078 s cm^-1 than M₁ (0.071 s cm^-1) at 7^th MAP stage. Among the sub-plot treatments, S₁₂ recorded the highest SDR of 0.099, 0.101, 0.109, 0.103 and 0.084 s cm^-1 at 3^rd, 5^th, 7^th, 9^th MAP and at harvest stages, followed by S₁₁ and S₁₀. The treatment S₁ showed a lowest stomatal diffusive resistance of 0.056, 0.052, 0.065, 0.059 and 0.039 s cm^-1 at all the growth stages. Interaction effects of M at S and S at M revealed significant difference at all the stages of growth.

Table 3 Effect of water stress on stomatal diffusive resistance (sec/cm) at different growth stages of banana cultivars and hybrids

Discussion

Turner D.W., 1990, Modelling demand for nitrogen in the banana, Acta Horticulturae, 275:4 97-503