INTRODUCTION

1. Genome Variability and Plant Age Influence Susceptibility to Moisture Stress in the Cultivated Bananas (Musa species) 1Baiyeri, K. P. and 2Ortese, E. 1Dept. of Crop Science, University of Nigeria, Nsukka, Nigeria. 2Akperan Orshi College of Agriculture, Yandev, Benue State, Nigeria. IeCAB2010 held on 1-15 June 2010

2. INTRODUCTION • Water stress is one of the major environmental constraints that limit crop productivity worldwide. • Consequent on climatic change, moisture availability (in terms of quantity, quality and duration) has become very unpredictable in most places. • Moisture availability has been identified as one of the most critical productivity determining factors in Musa species (Robinson and Bower, 1986;Turner et al., 2007). IeCAB2010 held on 1-15 June 2010

3. Introduction… • Water deficit imposes huge reductions in crop yield through diminished leaf carbon fixation and general growth inhibition. • However, the degree of plant susceptibility to transient or prolonged moisture deficits is somewhat dependent on the plant’s physiological growth stage during the time of water stress (Hall et al., 1981 ). • The deleterious effects of moisture stress in most species are more disastrous during the reproductive growth phase (Evans, 1993); another precarious stage is the juvenile seedling stage. IeCAB2010 held on 1-15 June 2010

4. Introduction … • Existing information suggests that hardiness in Musa species is influenced by genomic grouping. • The cultivated bananas (Musa species) comprise of three main genomic groups (AAA, AAB, ABB), but with the array of emerging improved genotypes, there is need to evaluate genomic responses to moisture stress with a view to identifying putative tolerant or less susceptible genotype(s). IeCAB2010 held on 1-15 June 2010

5. Objective To study the influence of plant age and genome composition on the susceptibility of Musa plants to transient drought condition. IeCAB2010 held on 1-15 June 2010

6. Materials and Methods • Experimental Site: The study was conducted in a glasshouse of the Department of Crop Science, University of Nigeria, Nsukka. Nsukka is located 6o 52′N, 7o 24′E and 447.2 m above sea level, in the derived savanna agro-ecology of Nigeria. • Design of Experiment: A six-week moisture stress period was imposed on six Musa genotypes comprising of two dessert bananas (AAA), two plantains (AAB) and two ABB cooking bananas at varying growth ages of 8, 12 or 16 weeks after planting. These were evaluated alongside the control (unstressed) plants in a 6 x 4 factorial in completely randomized design (CRD) of five replications. Each genomic group consisted of one landrace triploid (3x) and a hybrid tetraploid (4x) genotype. IeCAB2010 held on 1-15 June 2010

7. Materials and Methods … Treatment application: • Fairly uniform early sword suckers were used in the study; these were raised in 17 kg of topsoil. • At the specific age of introducing water stress, watering was withdrawn for six weeks and thereafter re-introduced for another six weeks. IeCAB2010 held on 1-15 June 2010

8. Data Collection and Analysis Growth changes in: • Plant height • Plant girth • Number of live leaves, and • Leaf area were evaluated after the six-week drought and rehydration cycles. All data collected were subjected to analysis of variance for factorials in CRD using GENSTAT Release 7.2 DE (GENSTAT, 2007). The separation of treatment means for significant effects was by least significant difference (LSD) at 5 percent probability level as described in Steel and Torrie (1980). IeCAB2010 held on 1-15 June 2010

9. Results Susceptibility to moisture stress varied with plant age, genome group and ploidy levels. • The effects of moisture stress were found to be most severe in the 16-week plants, whereas the 8- and 12-week-old plants had a fair tolerance. Considering the mean values across the six genotypes (Table 1), stress effects on leaf area, plant girth and number of live leaves were more severe on the 16-week-old plants. • The negative values observed in leaf area, plant height and girth in the 16-weeks plants after the stress (Table 1) and rehydration cycle (Table 2) are indications of shrinkage or outright loss of plant parts due to tissue desiccation. • The percentage survival values on Table 2 showed clearly that the 16-week-old plants were more susceptible to the transient drought. IeCAB2010 held on 1-15 June 2010

10. Results … The cooking bananas (ABB) and plantains (AAB) were more drought-tolerant than the AAA-dessert bananas. • The cooking bananas (‘Fougamou’ & ‘BITA 7’) and plantains (‘Agbagba’ & ‘PITA 22’) had a better growth recovery (Table 2) as evident from the higher values recorded in plant height, girth and number of leaves per plant after the rehydration period. • Besides, the dessert bananas had a very poor survival percentage, although the landrace genotypes ‘Agbagba’ and ‘Fougamou’ were equally affected. • Similarly, the landrace triploid genotypes were relatively more susceptible than the tetraploid hybrids. The mean values for number of leaves, leaf area and plant girth (Table 1) showed the landrace genotypes in plantains and dessert bananas to be more sensitive to moisture stress than the tetraploid counterparts. IeCAB2010 held on 1-15 June 2010

11. Table 1: Changes in growth parameters of six Musa genotypes exposed to moisture stress at 8, 12 & 16 weeks after planting.

12. Table 2: The recovery pattern and changes in growth components of six Musa genotypes exposed to moisture stress at varying ages estimated after a 6-week rehydration cycle.

13. Conclusion and application of findings • This study suggests that Musa crops at their early vegetative growth stage are more likely to withstand moisture stress than the older plants. Field planting and other cultural practices (like mulching and irrigation) should be conscientiously planned to avoid prolonged exposure of plants to drought, particularly at the reproductive transition phase. • The differential sensitivities of the genomic groups to the induced moisture stress makes breeding a viable option for upgrading drought resistance/tolerance in bananas in readiness for the apparent change in global climate. IeCAB2010 held on 1-15 June 2010