Pea (Pisum sativum L., Family: Leguminosae) is an important vegetable crop of tropics. It is grown all over the world for its fresh use, preservation, high level of digestibility which is more than most of the legumes. Dried peas have been found to contain 23.5% crude protein, 1.7% ether extract and 2.9% ash. Owning to great nutritional importance, cultivation of peas in the world is increasing. In Pakistan, Mateore, Green feast, Rondo and Climax are the main commercial varieties of peas. These are grown on an area of 91038 ha with a production of 53957 tons. National average yield of peas (576 kg ha-1) is considered to be the lowest in the world and it does not support the demands of country. There are various factors of low yield such as inappropriate agronomic practices, misuse of chemicals, use of unhealthy seeds and continuous mono-cropping.
Besides other causes of low yield, seed associated mycoflora also play an important role. Economically important seed associated mycoflora of peas are Alternaria sp., Aschochyta pisi, Fusarium sp., Aspergillus sp., Penicillium sp., Rhizoctonia sp., Bean yellow mosaic virus, Seed borne mosaic potty virus (PSbMV) and Pseudomonas syringeae pv. pisi.
In Pakistan, peas are subjected to many seed associated diseases, but so far very little information is available on the role of seed associated mycoflora in poor seed germination and over all yield. In the light of above knowledge this study was planned with following objectives:
||To see the fungal mycoflora associated with different pea
||To note the efficacy of different types of seed treatments
in increasing the germination %age and reducing infection %age of different
MATERIALS AND METHODS
Seed samples: Samples of three commercial varieties of peas (Matter Mateore Local, Matter Mateore Holland, and Rondo) were collected from vegetable seed stores and Horticultural Research Institute, National Agricultural Research Center, Islamabad. This experiment was conducted during 2002-2003.
Seed treatments: For each treatment a sample of 200 seeds of each variety was selected.
Treatment with chlorox: Seeds were first washed with distilled water then dipped in 1% chlorox solution for 2 min then again washed with distilled water and dried on blotter paper.
Hot water treatment: Seeds were soaked in sterilized distilled water for 5-10 min then placed in hot air oven at 53°C for 12-13 min. The seeds were then dried on blotter paper.
Treatment with fungicide: Vitavax was selected for fungicide treatment. First of all fungicide solution was prepared and then applied to seeds @ 1g kg-1 seeds. Seeds were soaked in fungicide solution for 3-4 min then dried on blotter paper.
Treatment with sterilized distilled water (kept as control): For treatment with sterilized distilled water, distilled water was sterilized at 121°C and 20-25 lb for 15-20 min.
Germination percentage: Germination percentage of all seed samples
by giving different treatments was noted by using standard rolled paper towel
method. Hundred seeds of each seed variety were selected randomly,
after giving different treatments seeds were dried on blotter paper and allowed
to germinate between two layers of blotter papers at 25±2oC
for twelve days under florescent day light tube. At the end of incubation, the
number of ungerminated and germinated seeds and seeds with abnormal mortality
Seed infection percentage: Seed infection percentage of three different pea varieties was counted by Blotter Paper method[8,9]. The seeds were sown in Petri dishes on moistened absorbent paper (blotter paper) after giving different types of treatments i.e., control, chlorox, hot water and fungicide treatment. Two hundreds seeds of each variety were placed at a fixed distance according to their size @ 10-16 per plate and incubated for a week at 20±2°C, the day and night cycle of 12/12 h was used under fluorescent light. The infection percentage was based on presence of the pathogenic signs of disease in/on the seedlings which may have germinated during incubation. Three successive readings were taken for 3 weeks.
Isolation, purification and identification of various fungi: To identify and purify fungal micro flora, fungi from seeds were cultured on potato dextrose agar medium (PDA). Fungal associations were examined under stereoscope. Identification of fungi was done with the aid of lab manual.
Efficacy of various treatments: Seed germination and infection percentage
pea seed samples was recorded with different treatments i.e., Clorox (1%), hot
water (52°C for 12-13 min), fungicide (Vitvax @ 1 g kg-1).
||Efficacy of various treatments in increasing germination %
and decreasing infection %
|*Any two means not sharing a common letter(s) differ significantly
(p = 0.05), **Average of three weeks data
|| Comparison of different verities of peas
|*Any two means not sharing a common letter(s) differ significantly
**MML stands for Matter meteor local and MMH stands for Matter Meteor Holland.
|| Impact of various microflora on germination %age of peas
|Average decrease in germination %age of 3 varieties=17.7%
*Chlorox, Hot water and fungicide treatments.
**Just washed with distilled sterilized water.
|| Mutter meteor Holland
Germination percentage was highest in case of fungicide treatment in all pea
seed samples i.e., 95.33% as compared to control i.e., 75%. Seed infection percentage
successfully increased from 1st to 3rd week. Least infection percentage was
observed in case of fungicide treatment (Vitvax @ 1 g kg-1) i.e.,
46.7% as compared to control i.e., 61.7% (Table 1).
|| Mutter meteor local
Seed associated mycoflora had significant impact on germination percentage
of peas and were found to cause an average decrease of 17.7% in germination
percentage of different pea varieties (Table 3).
Incidence of various mycoflora: Twelve species of various mycoflora were found to be associated with pea seed samples of different varieties. These include Alternaria sp., Aspergillus sp., Candida sp., Chetomium sp., Cladosporium sp., Curvularia sp., Drechslera sp., Fusarium sp., Monilia sp., Penicillium sp., Rhizopus sp., Cephalosporium sp., (Fig. 1-3). Out of these, five fungi i.e., Alternaria sp., Fusarium sp., Aspergillus sp., Penicillium sp. and Rhizopus sp., were found in high frequencies and among them Alternaria sp., had highest frequency i.e., 38, 27 and 67% in pea varieties Matter Mateore Local, Matter Mateore Holland and Rondo variety, respectively in control (Fig. 1-3).
Comparison of different pea varieties: Among three varieties of peas, Matter Mateore Local proved to be more resistant by showing highest germination percentage i.e., 92% and least infection percentage i.e., 44.25% and it showed least incidence of various mycoflora as compared to other two varieties. Rondo variety showed highest infection percentage i.e., 78.03% and highest incidence of various mycoflora with minimum germination percentage i.e., 855% (Table 2).
All treatments were found to be significant in increasing germination percentage but not so much significant in reducing infection percentage.
Treatment with fungicide i.e., Vitavax @ 1 g kg-1 proved to be most effective. Vitavax is a systemic fungicide. Ahmad et al. found that treatment with Vitavax @ 2 g kg-1 give 87.50% germination with 5724.45 kg ha-1 dry grain yield in maize as compared to control with 15.2% germination and 4835.56 kg ha-1 dry grain yield. It has also been reported to increase germination percentage upto 25.37% in sorghum and 53% reduction in seed associated Fusarium solani in onion. Chlorox and hot water treatment were not found to be effective as fungicide (Vitavax 1 g kg-1 of seed) because chlorox is only surface disinfectant, while hot water treatment is effective mostly for nematodes, most of the fungal spores are above to survive even after hot water treatments.
Efficacy of Vitavax @ 1g kg-1 confirmed the findings of Ahmad et al., Javed et al., Haq and Khan.
High incidence of Alternaria sp., Fusarium sp., Aspergillus sp., Penicillium sp. and Rhizopus sp. shows the economic importance of these mycoflora and confirm the findings of Hagedorn, Czyzewka and Anwar et al.. Alternaria sp., is one of the most economically important mycoflora associated with pea seed and plays a significant role in reducing over all vigor and yield of peas. Fusarium sp., also has a significant role in reducing germination percentage and over all yield of peas. While saprobes like Aspergillus sp., Penicillium sp., and Rhizopus sp., associated with pea seeds also play an important role in seed germination by producing toxins. Seed associated mycoflora had significant impact on germination percentage of peas and were found to cause an average decrease of 17.7% in germination percentage of different pea varieties (Table 2). This confirmed the findings of Susuri et al. and Anwar et al..
Highest germination percentage, least infection percentage and incidence of various mycoflora in pea variety Matter Mateore Local showed increased resistance of local varieties as compared to exotic verities and this demands need of more research to utilize the potential of local material.
This study shows the impact of various mycoflora on germination of pea seeds and efficacy of various treatments for its control and it will be helpful in doing more research regarding seed pathology of peas.