Introduction
Plant diseases produce serious losses to peanut; an important leguminous crop in the third world. Of these, the disease transmitted through seed produce seed rot and affects the germinability of seed. Since fungicides used for the control of seed-borne diseases are hazardous to human health and environment, there is a need to develop alternative methods of plant disease control. During the course of our previous studies, a number of antioxidant were found effective in the control of seed-borne pathogens viz., Cephalosporium sp, Fusarium moniliforme, F. oxysporum, F. solani, Rhizoctonia solani, Sclerotium bataticola and Verticillum sp., which produce serious losses to peanut crop in Egypt. Soaking of seeds in 20 mM water solution of hydroquinone for 12 h before planting significantly decreased pre-emergence and post-emergence damping off caused by the seed-borne pathogens. Seedlings survival and plant vigor also showed an increase (Elwakil and El-Metwally, 2000).
Peanut seeds infected by seed-borne fungi have been reported to produce seed abortion, shrunken seeds, reduce seed size, seed rot, sclerotization of seeds, seed necrosis, seed discoloration, reduction of germination capacity and physiological alternation of seed (Neergaard, 1979). Considering the importance of peanuts as an important cash crop due to high quality of edible oil and protein, the peanut cultivated area in Egypt has increased 5 fold in 12 years from 12.327 ha in 1990 to 60.329 ha in 2001 (Anonymous, 2001). There is therefore need for an effective method for controlling seed-borne diseases of peanut with emphasis on the use of antioxidants which would not have adverse effect on the environment as compared to use of pesticides.
Due to the unique and sole growth manner of peanut seed, the prevalence of its infection by pathogens continue to increase. This attributes to the up-growth of seed in the soil which is usually full with soil inhabiting pathogens and these may attack seed at different stages of its growth. Subsequently, in the present study, an attempt has been made to use the antioxidant hydroquinone, instead of seed treatment by chemicals, not only to reduce the incidence of seed-borne fungi develop during the up-growth but also to improve the seeds of peanut qualitatively and quantitatively.
Materials and Methods
Seed samples
Peanut seed lot cv. Giza 4 which showed the presence of Cephalosporium
sp, Fusarium moniliforme, F. oxysporum, F. solani, Rhizoctonia solani, Sclerotium
bataticola and Verticillum sp., was used in this investigation.
Antioxidant
Hydroquinone was dissolved in tap water at 20 mM concentration and used
for soaking peanut seeds for 12 h. The seeds were then air-dried for 2 h before
planting.
Field trials
Four different plots containing sandy soil, each of one acre, located in
the northern coast of Egypt (Dakhlia and Behera) were selected for this study.
Seed treatment
Seeds were treated for 12 h in 20mM hydroquinone then air dried for 2 h
and sown in the selected field plots. Untreated seeds were soaked in tap water
for 12 h and air dried for 2 h before sowing. All the recommended methods of
planting, watering as well as agricultural practices including weed control
were followed. No fertilizers were applied.
Harvesting
By the end of October 2001, plants were removed and the growth parameters
including plant height, root and shoot length, plant weight, root and shoot
weight, number of branches, pegs and pods, dry weight of the plant and yield
were calculated.
| Table 1: |
Growth parameters and yield of peanut raised from Hydroquinone
treated seeds. |
 |
| *Within rows, means followed by different letters are significantly
different at the 0.05 probability level |
| Table 2: |
Presence of fungi in seed samples after treatment with or
without hydroquinone |
 |
| 1Check= Seeds harvested from the cultivated hydoquinone-untreated
seeds |
| 2 Hydroquinone= Seeds harvested from the cultivated
infected seeds but treated with hydroquinone before sowing. |
| 3 Within rows, means followed by different letters
are significantly different at the 0.05 probability level. |
Statistical analysis:
The data were analysed using analysis of variance (GLM procedure in PC-SAS
software release 6:11; SAS Institute Inc., Cary, NC, USA.) using Duncan’s
multiple range test (DMRT) for treatment means comparisons.
Results
Treatment of peanut seeds with hydroquinone showed an increase in plant height, root length, shoot length, root fresh weight, shoot fresh weight, number of branches, pegs and pods per plant. Dry weight of the plants also increased. It is interesting to note that hydroquinone treatment showed a 50% increase in yield (Table 1, Fig. 1 and 2).
|
| Fig. 1: |
Pod production of plant raised from peanut seed (A) untreated
(B) treated with 20 mM hydroquinone |
|
| Fig. 2: |
Production of pods and seeds of one plant of peanut (A) raised
from untreated seed, (B) treated with 20 mM hydroquinone |
Seed health testing of the produced seeds
The harvested seeds of plants raised from hydroquinone treatment as well
as from the check were examined for the presence of seed-borne fungi. Infection
% of seed-borne fungi was considerably reduced in treatments where hydroquinone
was used as compared to untreated seeds (Table 2). Rhizoctonia
solani, Cephalosporium sp., Bipolaris sp., were completely
inhibited in the hydroquinone treatment.
Discussion
The results of the present study would suggest that alternative methods for plant disease control especially of edible and underground produced peanut seeds should be exploited instead of indiscriminate use of pesticides which show harmful effects on human health and environment. The previous research by the author showed that the antioxidant hydroquinone is a promising safe chemical for controlling the seed-borne fungi of peanut. The present study showed that hydroquinone not only inhibits the seed-borne fungi but also has an effect in improving the growth of the plants and raise the yield by up to 50% more comparing to the untreated treatments. This phenomenon has also been shown by Chinese authors (Boeckx, et al., 2000) who indicated that hydroquinone function as urease inhibitor and improve the urea N recovery by spring wheat with 34% as compared to the treatment where only urea was applied. It also improved the quality (protein N content) of the grain. Moreover, antioxidants play an important role in expression of resistance in plant to pathogen attack (Larson, 1995; Jalali et al., 1999). This mutual effect for controlling the mycotoxin producing fungi as well as producing good quality seeds and raising the production by up to 50% is to be considered by the growers. The method is safe, simple, applicable and not costly. Hydroquinone (20 mM) which has a very low toxicity, Toxicity III, (Richard, 1995) may prove to have a significant effect in peanut production in future.
Acknowledgment
Thanks to Prof. Dr. Abdul Ghaffar, Professor (Retd.) Department of Botany, University of Karachi, Karachi-75270, Pakistan, for his critical review of the manuscript.
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