Chickpea

Action time line

30 NOV 2009

Title

Gametophytic selection in chick Pea

Abstract

An investigation was made to study the in vitro response of pollen and its association with the sporophytic level for moisture stress tolerance in twelve chickpea genotypes under normal and simulated field conditions. Poly Ethylene Glycol (PEG 6000) based osmatic stress was created by treatment ranging from 5 - 20% in the pollen germination medium (PGM). The highest pollen germination per cent and tube growth was observed in 8% PEG, while the lowest was at 16%. The increase in the PEG concentration in the PGM, significantly reduced the per cent pollen germination and the tube growth in all the chickpea genotypes. The reduction in in vitro per cent pollen germination and the tube growth due to increased PEG concentration was evident in highly susceptible genotypes viz., JG 62 and WR315 than moisture stress tolerant genotypes viz., Karikadle and ICC 4958. Correlation analysis between gametophytic and sporophytic reactions for moisture stress tolerance of the chickpea genotypes revealed that, PEG required to inhibit 50% of pollen germination and the tube growth was positively associated with the seed yield under moisture stress treatment both in normal and late sown conditions.

and negatively associated with the seed yield difference between non-stress and stress treatment and drought susceptible index (DSI) in both normal and late sown conditions. 

The association between pollen and the sporophytic reaction to the moisture stress indicated the possibility of rapid screening of large number of genotypes by means of pollen assay as an alternate technique with regard to sporophytic moisture stress tolerance in chickpea.

Keywords

Keywords: moisture stress, pollen germination, Poly Ethylene Glycol, drought susceptible index, gametophytic selection

Introduction

Cicer arietinum L., is popularly known as chickpea, the third most important grain legume in the world after dry beans and dry peas that brings about a formidable solution to the alarming problems of protein scarcity of the world. Chickpea is indispensable to Indian agriculture as a predominant source of protein for vegetarian population (Arora, 1988). As pulses packs two to three times more energy rich proteins and oil in their seeds compared to cereals. Their amino acid pattern is rich with lysine content and complements the deficiency profile of cereals admirably; So pulses has been named as poor man’s meat and rich man’s vegetable.100 g seeds of chickpea constitute 396 Kcal of energy, 19.4 g of protein, 5.5 g of fat, 280 mg of calcium, 12.3 mg of iron and 301 mg of phosphorus. This crop has been named as poor man’s meat and rich man’s vegetable.

Most of the promising chickpea tested in the national network have shown potential yield of 2000 to 2500 kg/ha, where as the national average still languishes at 750 to 850 kg/ha (Masood Ali and Shivkumar, 2001). The major factors contributing to low yield in the country especially in southern states are the short period available for the crop growth and incidence of terminal drought accompanied with other biotic stress. Although the progress towards alleviating biotic stress affecting chickpea productivity has been satisfactory, the work on abiotic stresses needs immediate attention. The most important abiotic stress is the drought, which severely affect the productivity of chickpea under rainfed production system.

The moisture stress affects almost all biophysical and biochemical process, the crop growth and the final yield. The irrigation is not the only answer to the problem. However/despite many decades of research, drought continues to be a major challenge to agricultural scientists. This is due to unpredictability of its occurrence, severity, timing and duration; and to the interaction of drought with other abiotic stress, particularly extreme of temperature and variation in nutrient availability and with biotic stress.

Inspite of plant’s genetic make up and optimum population, breeding has not been as effective on different agronomic parameters of the crop under drought stress conditions as it has in their absence. More over, breeding for drought resistance is very frustrating. To quote Arnon (1980), “Breeding for drought resistance has been a consistent theme for as long as I remember and probably the greatest source of wasted breeding efforts in whole field of plant breeding”. The physiological process also cause set a limit on yield. Many techniques give quantitative estimation of morphological changes that takes place during the growth of crop and provides some insight in to the physiological variation in yield caused either genetically or by environment. The development of ideotype concept by Donald (1968) attempt is being made in chickpea to hypothesize and develop an ideal plant type. The greater awareness of the role of early vigour, root characters along with morpho-physiological parameters and extent of genetic variability and association of these parameters with yield and its component traits, which is pre requisite for success of chickpea drought resistance breeding programme in deriving an ideal plant type is now being increasingly felt. It is also important to investigate and examine the nature. However, the improvement in productivity of different crops based on selection at sporophytic level has been far below satisfactory, because of epistatic interaction in the expression of the resistant traits and genotype x environment interactions. In view of these difficulties several attempts have been made in the recent past to evolve alternate approaches to breed for drought. One of these involves the use of male gametophytic selection

Selection at gametic stage is rapid and offers opportunities to screen large number of genotypes. The impetus for screening at the gametic stage emerged in late 1970’s after the discovering that nearly 60 per cent of the genes expressed in the gametes overlap with that expressed in the sporophyte. In other words screening and selection for traits such as resistance at the gametic stage would be relevant at the sporophytic stage. The technique itself is an extension of what normally occurs in nature, where because pollen grain number per stigma generally, exceeds the number of ovules per ovary.

Employing selection at the gametic stage, a number of workers have developed genotypes tolerant to biotic and abiotic stress such as high temperature in tobacco (Mandhu Bajaj et al., 1988) and in tomato (Sato and Peet, 2004), Alternaria leaf spot in sunflower (Chikodi and Ravikumar, 2000), drought in sorghum (Ravikumar et al., 2003 and Patil et al., 2005), cold in chickpea (Clarke et al., 2004) and tomato (Dominguez et al., 2005).

The present study aims to develop suitable in vitro technique to screen pollen grains for tolerance to moisture stress in chickpea and to estimate the degree of association between gametophytic and sporophytic for tolerance to moisture stress.

Materials and methods

Twelve chickpea genotypes showing different levels of susceptibility to moisture stress were selected viz., K-850, ICC4958, WR-315, Karikadle, Annigere-1, BG256, ICC-96029, JG 62, ICCV-10, ICCV-2, WK-04-83 and WK-04-33. These genotypes were evaluated for moisture stress and non stress treatments by replicating twice for each treatment.

The experiments were conducted under normal and late rabi season under depleting moisture conditions. There was no rain during the crop growth period from sowing to harvest (except 5.4 mm of rain fall in the month of December). The rain fall in the preceding season (kharif) prior to sowing was 304.5mm, which was below normal (647.5mm) suggesting that the experiments were subjected to high level of moisture stress for the study. The moisture stress was created by withholding irrigation after germination and seedling establishment. For the non stress treatment, irrigation was given at regular intervals up to physiological maturity. All the recommended package of practices were adapted for raising the crop. The seed yield and yield components were recorded (here mentioned only on yield) on randomly selected five plants in each genotype per replication and the main treatment.

B. In vitro PEG treatment of pollen

The standardized pollen Germination Medium of chickpea composed of MnSO4 (200mg/l), Ca (NO3)2H2O (200mg/l), Boric Acid (100mg/l), KNO3 (100mg/l) and 10% PEG (Poly Ethylene Glycol-6000, a non permeant osmoticum is one of the important component of the Pollen Germination Medium) was taken as a control. Different levels of moisture stress was created by treating the pollen with different levels of PEG concentrations. With the increase in PEG concentration will decrease the water potential there by increases the osmotic stress in the PGM. In order to study the effect of moisture stress on pollen germination and the tube growth, different PEG concentrations were used as different treatments viz.,8, 10, 12, 14 and 16% in the PGM. The pollen grains of selected twelve genotypes were tested for % of pollen germination and pollen tube growth.

C. In vitro pollen screening for moisture stress tolerance

The most viable pollen grains of one-fourth to half opened flower buds were collected from the field grown chickpea plants of twelve genotypes. These pollen grains were dusted uniformly on to the cavity slides having 50µ Medium of different PEG treatments. For each treatment and genotype, five replications were maintained. These were incubated at room temperature in Petri dishes with moist blotting paper on both the sides to maintain a relative humidity of 70-80%. Observation was recorded after 45 minutes of incubation by staining with Acetocarmine. For each replication six fields were chosen randomly for recording observation on % pollen germination and the tube growth under projection microscope. From this experiment following parameters were determined. Pollen germination and the tube growth at different levels of PEG was expressed as percent of control PEG concentration required to inhibit 50% of % pollen germination and the tube growth using MSTAT Probit analysis. Identification of moisture stress tolerant chickpea genotype through pollen screening.

Statistical analysis:

The differential response of genotypes to moisture stress at both sporophytic and gametophytic level was statistically tested by rank correlation analysis. The effect of moisture stress on pollen parameters (% pollen germination and the tube growth) and various sporophytic parameters (Seed yield in moisture stress and non stress treatment and its difference along with DSI (Drought Susceptibility Index) of both normal and late sown experiments) of each genotype was determined by calculating correlation coefficients to study the strength on relationship between gametophytic and sporophytic tolerance to moisture stress, correlation between PEG required to inhibit 50% of % pollen germination and the tube growth with sporophytic parameters were determined.