Advances in Agricultural Science 05 (2017), 02: 10-14
Impact of Azolla caroliniana and A. pinnata as soil amendments on Rotylenchulus reniformis and plant growth of cowpea in Egypt
Ahmed El-Sayed Ismail 1*
1Department of Plant Pathology, National Research Center, Dokki, 12622, Giza, Egypt.
Two Azolla species, Azolla caroliniana and A. pinnata were evaluated throughout two successive seasons (2015 & 2016) as green manures on Rotylenchulus reniformis and plant growth of cowpea cv. Baladi under greenhouse conditions (25±5°C). The substrates were applied at the rates of 25 and 50 gm of dry material of each species / pot. The use of A. caroliniana and A. pinnata significantly (P = 0.05, 0.01 levels) succeeded in reducing the number of swollen females and number of egg-laying females and also significantly (P = 0.05, 0.01 levels) improved cowpea growth when compared with those of the check. The use of A. pinnata significantly (P = 0.05, 0.01 levels) reduced the number of swollen females and number of egg-laying females per plant, at both rates, when compared to A. caroliniana. Also, the growth of cowpea plants was affected due to the application of Azolla. Addition of Azolla to the plant caused a remarkable increase in the cowpea growth. The higher dose of each Azolla species was significantly (P = 0.05, 0.01 levels) more effective than the lower one. In general, the use of dry materials of A. pinnata resulted in increase in the plant growth, more than A. caroliniana.
The reniform nematode, Rotylenchulus reniformis attacks a wide range of crops including cowpea, Vigna sinensis in Egypt as well as in many parts of the world (Oteifa, 1987 and Johnson & Fassuliutis, 1984). Therefore, management of this nematode has received attention to reduce damage. However, hazards resulting from synthetic nematicides have encouraged scientists to search for alternatives. A free floating water fern commonly known as azolla or mosquito fern or duckweed fern or fairy moss heavily grows on water surface and fixes atmospheric nitrogen. Some studies have been devoted to utilize Azolla plants as a bio-fertilizers in management different plant-parasitic nematodes i.e. Pratylenchus penetrans, Heterodera glycines, Meloidogyne incognita, Tylenchorhynchus vulgaris, M. incognita and M. javanica in soil (Walker, 1969, Barker et al., 1971, Thaker et al., 1988, Patel and Thaker, 1989 and Patel et al., 1994 , Abadir and El-Hamawi, 1995 and Ismail, 2015; respectively).Therefore, the aim of the present work wasto compare the effective role of two species of Azolla plants namely A. caroliniana and A. pinnata as soil additives in suppressing the reniform nematode, Rotylenchulus reniformis infecting cowpea throughout two successive seasons (2015 & 2016) under greenhouse conditions in Egypt.
Materials and Methods
Seeds of cowpea, Vigna sinensis cv. Baladi were sown in 15 cm diam. plastic pots filled with 1 kg autoclaved sandy loam soil (1:1 w/w) with pH 7.3 and E.C. 0.56 throughout two successive seasons (2015 & 2016). After germination, the seedlings in each pot were thinned to one seedling / pot. Two species of Azolla plants namely, A. caroliniana and A. pinnata were air dried under shade for 2 weeks and finally powdered by an electric grinder and thoroughly incorporated with the soil as soil amendments at two rates i.e. 25 and 50 gm / pot of each species. The pure culture of Azolla plants were obtained from Plant Nutrition Department, Institute of Soil and Water Research, Agricultural Research Center (ARC), Giza, Egypt. The dry Azolla rates of each species were added two weeks before seeding to allow their decomposing in the soil. The chemical analyses of the tested Azolla species are shown in table (1). The treatments were replicated five times. Untreated pots served as control. The pots were arranged in a greenhouse bench in a completely randomized block design (25± 5 ºC) and irrigated with tap water as needed. One thousand of infective stage ( J4) of R. renoformis (equivalent one J4 per one gm soil ) were poured into three holes at the base of the standing plant 15 days after germination.The nematode inoculum was obtained from tomato (Lycopersicon esculentum L. cv. Super Strain B) roots .After dissolving the gelatinous matrix of the nematode egg masses using sodium hypochlorite solution, centrifuging and washing with tap water, the nematode suspension was left in aerated water for three days at 27 ± 2ºC and then examined under stereomicroscope to confirm that all viable eggs had hatched just before application. Seventy days after the nematode inoculation time, cowpea plants were carefully uprooted and nematodes in pot soil and on cowpea roots were determined. The nematode juveniles in the soil were extracted by sieving and decanting method (Barker, 1985). Also,the number of swollen females / root and egg- laying females / root were determined. All plant growth parameters e.g. lengths, fresh weights and dry weights of both root and shootwere recorded. Percentages of plant growth increase based on shoot and root fresh weights and percentages of nematode reduction as compared to untreated pots were calculated .
In both experiments, the obtained data on cowpea growth components (lengths and fresh weights of both shoot and root growth) were collected. Data were also collected on number of larvae in soil, both females and egg-laying females on roots from all the treatments. All the data were pooled together and means were analyzed statistically using the Fisher,s Least Significant Difference (L.S.D.) according to Gomez and Gomez (1984).Correlation analyses were also used to determine the relationships between doses of tested substances, each of decreases in the different nematode stages and increases in the cowpea growth components.
Results and Discussion
When dry Azolla additives of both species were incorporatedinto soil of cowpea plants cv. Baladi fourteen days before seeding, it significantly (P = 0.05 and or 0.01 levels) affected on development and reproduction of R. reniformis as compared to the check plants (Table 2). Clearly, Azolla pinnata was significantly (P = 0.05 and or 0.01 levels) reducing all the nematode stages as compared with A. caroliniana did. Both Azolla species significantly (P = 0.05 and or 0.01 levels) decreasing swollen females / root, egg- laying females / root and the
Table 1. Chemical analyses of the tested Azolla species.
*pH= 1: 2.5 Azolla: water ratio, E.C. = Electrical conductivity (m mhos / cm 2)
Table 2. Effect of Azolla caroliniana and A. pinnataas dry soil additives on the final population of Rotylenchulus reniformis infecting cowpea. (Mean of two successive seasons, 2015 & 2016)
Treatments & rates
No. of swollen females / root
No. of egg-laying females / root
No. of juveniles in soil / pot
25 g / pot
50 g / pot
25 g / pot
50 g / pot
Table 3. Cowpea growth as influenced with dry soil additives of Azolla caroliniana and A. pinnata and infected with Rotylenchulus reniformis. (Mean of two successive seasons, 2015 & 2016)
Treatments & rates
Fresh weights (g)
Dry weights (g)
25 g / pot
50 g / pot
25 g / pot
50 g / pot
Inc. = Increase %.
juveniles in soil when compared with those of the control. Significantly (P = 0.05 and or 0.01 levels) increasewas attainedwith increasing the evaluated rates of Azolla. So, swollen females was highly affected by using the higher rate (50 gm / pot) of each azolla species than the lower one (25 gm /pot), as was significantly (p = 0.05 or 0.01)reduced by 45.5% and 26.8%, or by 76.4% and 36.2% when the soil was amended with A. caroliniana or A. pinnata; respectively (Table 2). The reproductive potential of the nematode was significantly decreased when soil was treated with either A. caroliniana or A. pinnata. Evidently, decrease in number of swollen females/ root, egg- laying females / root as well as number of juveniles in soil was attained by using the different rates of Azolla plants as compared to the control. The application of dry substrates of A. pinnata treatment was significantly (P = 0.05 and or 0.01 levels) more effective than A. caroliniana. Also, a pronounced difference was observed between the rates of both Azolla species. As shown in Table 2, percentages of reduction in number of egg- laying females / root ofA. caroliniana treatments were 36.0 % and 63.3% for the lower and higher rates; respectively; while they were 69.1 and 71.9% for the lower and higher rates of A. pinnata; respectively.
Cowpea plants showed luxuriant growth due to soil amending with dry Azolla plants. The two rates significantly (P = 0.05 and or 0.01 levels) increased plant growth criteria’s (Table 3). A positive trend was detected between the plant growth increase and the used rates of both Azolla species. Application of dry materials of A. pinnata was significantly (P = 0.05 and or 0.01 levels) more effective than A. caroliniana, and the higher rates were, also, more effective than the lower ones as shown in Table 2.The present results proved the activity of Azolla plants in eliminating the reniform nematode population and improved the cowpea growth when used as soil additives. Some studies stated that the highly nutritive components of such plants from minerals such as calcium, phosphorus, potassium, sodium, magnesium, manganese, zinc, copper and iron as well as amino acids e.g. alanine, arginine, aspartic acid, cystine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine could significantly adversely interfere on the development and reproduction of the nematode (Thomas et al., 1980 and Francisco et al., 2000). Consequently, the decomposing dry Azolla plants as green manures could help in improving the plant growth. Similar results has been attained by Patel et al. (1989 & 1994) as they found that dry A. pinnataas soil additives reduced the stunt nematode, Tylenchorhynchus vulgaris population and consequently improving the plant growth, as well as, Ismail (2015) found that both of A. caroliniana and A. pinnata as green manures reduced the root-knot nematode, M. javanica and improving the tomato growth. Fresh materials of both A. filiculoides and A. pinnata decreased M. incognita and improved the plant growth (Abadir and El-Hamawi, 1995). Moreover, the extracts of both fresh and dryA. Pinnata plants inhibited egg hatching of M. javanica and M. incognita (Thaker et al., 1988). Further studies are needed to clearly elucidate proper effect against plant-parasitic nematodes.
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