«D. ANITHA KUMARI THESIS SUBMITTED TO THE ACHARYA N.G RANGA AGRICULTURAL UNIVERSITY COLLEGE OF AGRICULTURE, RAJENDRANAGAR IN PARTIAI FULFILLMENT OF ...»
grain legumes grown between 30% and 30's in the semi arid tropics (Nene et al., 1990). It is an important source of high quality dietary protein and is mostly consumed in the form of split pulse. It plays a significant role in the nutritional security of the overwhelming majority of vegetarian people of the Indian Subcontinent. More than 150 insect species feed on this crop, of which pod borer, Helicoverpa armigera (Hubner) is the most damaging pest worldwide (Shanower el al., 1999). The pest can cause complete crop loss (Reed and Lateef, 1990).
H. armigera damage is particularly severe in indeterminate plant types than in determinate ones (Reed and Lateef, 1990). Over the past decade, three outbreaks of this pest were recorded, the latest being in 1997 in Gulburga, which is known as the pulse bowl of Kamataka. H.armigera causes 50 to 60% grain loss in pigeonpea.
During 1997-98, the pigeonpea suffered a complete loss due to H. armigera (Puri, 1998). On an average, pod borer caused 90 - 100% yield loss in 1992-93 and 1997Yelshetty and Gowda, 1998). In the semi-arid tropics, pod borer cause an estimated loss of US$325 millions annually (ICRISAT, 1999).
Pigeonpea is mainly grown during the rainy season. Traditionally
also be maintained as perennials (Nene el al., 1990). In the recent years, there is increasing emphasis on short-duration cultivars, in which the first flush of pods can mature in 90 to 120 days (Chauhan, 1990). Such cultivars are grown in rotation with wheat and other winter crops in northern (Singh., 1996; Dahiya er a[.. 2001), central and peninsular India (Nam el al., 1993). Pigeonpea is grown on relatively poor soils, and has the potential to provide upto three crops per year (Rangarao and Shanower, 1999). In India, pigeonpea is grown on 3.2 million hectares with an annual production of 2.48 million tonnes and accounts for 85 to 90% of the worlds area under pigeonpea (FAO, 2001). Pigeonpea yields have remained stagnant for the past three to four decades, largely due to insect pest damage.
H. armigera has a wide host range, and feeds on more than 300 plant species, of which pigeonpea is highly preferred. Prior to 1975, less than 20% farmers used insecticides on pigeonpea. However, 1993 onwards, there is a widespread adoption of insecticides for pest management on pigeonpea. Due to widespread use of insecticides, it has developed considerable levels of resistance to conventional insecticides, including synthetic pyrethriods (Armes et a1.,1992).
Natural enemy activity on H,armigera in pigeonpea is quite low as compared to that on other crops such as sorghum (Bhatnagar er al., 1980). As a result, there is greater survival of the insect on pigeonpea and results in heavy loss in grain yield.
mechanisms against insect pests. The major mechanisms are antixenosis (nonpreference), antibiosis, tolerance, and escape (Painter, 1951). These mechanisms are operational within the plant through different component traits. Using specific assays to monitor the effects of particular physical and chemical characteristics on insect behaviow and physiology, resistance has been differentiated in terms of antixenosis, antibiosis and tolerance. T o date, more antibiosis than antixenosis or tolerance has been reported in legume crops (Clement et al., 1994).
under subsistence farming, and is largely beyond the means of resource for poor farmers Therefore, host plant resistance (HF'R) assumes a pivotal role in controlling H,armigera damage either alone or in combination with other methods of control.
HPR is an important component of integrated pest management (LPM), and is well suited to the environmental conditions of the semi-arid tropics. Host plant resistance avoids environmental pollution and is compatible with natural control measures Besides, it integrates effectively with other pest control tactics, and involves no additional cost to the fanner It has been documented that for each $1 invested in plant resistance, farmers have realized a $300 return (Robinson, 1996).
The identification and utilization of cultivars resistant/tolerant to H,armigera would have a number of advantages, particularly for a relatively lowvalue crop such as pigeonpea. Screening of germplasm (more than 14,000 pigeonpea accessions) for resistance to H.armigera has revealed very low levels of resistance to this pest (Reed and Lateef, 1990). Several lines of pigeonpea such as ICPL 7703, ICPL 332, ICPL 87088, ICPL 84060 and ICPL 87089 with low to moderate levels of resistance have been identified (Lateef, 1992; Sachan, 1992).
suffered 7% damage by H. armrgera compared to 16% damage on ICPL 187-1, 30% on ICPL 332, and 76% on ICPL 87 (ICRISAT, 1999). However, these germplasm lines have not been characterized for diversity and mechanisms of resistance to this insect Although several genotypes with resistance to H. armrgera have been reported, little progress has been made in incorporating resistance into cultivars with acceptable grain yield and quality., Wild relatives of Cajanus cajan are also a potentially valuable source of germplasm for improving resistance or tolerance to insect pests in pigeonpea (Pundhir and Singh, 1987).
and pods. When periods of H. armigera activity occur during vegetative stages, significant amount of leaf feeding can occur. However, once flowering commences, feeding occurs preferentially on reproductive plant parts. The usual sequence followed by a H, armigera on pigeonpea appears to be for moth to lay eggs on flowers, young pods or leaves in the upper part of the crop.
slowly on artificial diet containing Cajanus scarabaeoides pod powder than C. cajan pod powder due to antifeedant or growth inhibiting compounds and/ or poorer nutritional quality of the wild species.
involved is essential for effective utilization of sources of resistance in the breeding programs. Despite large scale screening of the germplasm, it has been felt that there is a scope for substantially improving HPR in pigeonpea to H.armigera, through a comprehensive understanding of the mechanisms by which the pod borer is either attracted to or repelled from pigeonpea.
chemical, and visual stimuli. Some possible physical deterrents may be pod wall thickness and hairs on the pod. Trichomes and their extracts and/or pod surface chemicals may also provide some protection against H,armigera feeding damage.
Acetone extracts of C. scarabaeoides pod surface include a weak, but significant feeding inhibitor (Romeis, 1997).
Cajanus scarabaeoides has been reported to be highly resistant to H. armigera (Lateef et al., 1981; Saxena et al., 1990; Shanower ef al., 1997).
Larvae feeding on flowers and green pods of C, scarabaeoides grow slower, take longer to pupate, and form smaller pupae than those fed on C. cajan (Lateef er al., 1981; Shanower et al., 1997). A high density of pod surface trichomes, a tough pod wall, and differences in the structure of pod tissue may contribute to the poorer growth of H.armigera compared with C. cajan (Lateef et al., 1981; Romeis el al., 1999a). In addition to physical factors, chemicals in or on the pods may also contribute to C, scarabaeoides resistance to H. armigera. Once the particular
systematic attempts can be made to incorporate these characteristics into high yielding cultivars. To elucidate some of the mechanisms involved in H,armigera resistance in pigeonpea, the present investigations were undertaken.
1. To evaluate the pigeonpea genotypes for the levels and stability of resistance
2. To characterize the sources of resistance for oviposition, non-preference, antibiosis and tolerance components of resistance.
3. To quantify the relative contribution of different components towards resistance to the pod borer.
Pigeonpea is an important grain legume endowed with several unique characteristics, finds an important place under subsistence farming systems in the semi-arid tropics. Pigeonpea seed protein content containing about 2% compares well with that of other important grain legumes (Nene el al., 1990). Insect pests feeding on flowers and pods cause the severe damage of which Helicoverpa armigera (Hubner) is the most important world wide. The larvae feed on buds, flowers, and pods of pigeonpea, and when these are not available, they feed on young leaves (Reed el al., 1989).
carried out at ICRISAT (Lateef and Pimbert, 1990). In general, determinate genotypes show greater susceptibility to pod damage by H. amigera than indeterminate types (Kushwaha and Malik 1987; Reed and Lateef, 1990) One of the reasons for high susceptibility of determinate type genotype to H. armigera may be due to cluster type of flowering making it easier for larvae to move from one pod Within short duration determinate types, ICPL 289 and H 81-95 to another.
(Kushwaha and Malik, 1987) have shown less susceptibility to pod borer (Dahiya el al., 2001). Among the medium- duration types, most of genotypes have
susceptibility to pod borer (Lateef and Pimbert, 1990). Short duration varieties (1 50 days) are safer from pod borer than extra early varieties (Singh, 1996).
Even though various chemical control measures have been devised to minimize the losses caused by pod borer, this pest has developed resistance to insecticides. Further, even from ecological and economical view point, cultivars having resistance to the pest is the most important component of IPM. It has been documented that with each $1 invested in plant resistance, farmers have realized returns of $300 (Robinson, 1996).
and are laid singly. The larva leaves the plant in 3 weeks or less, and bores into the soil to a depth of 1.5 to 2.5 cm, where it pupates. The pupa is 14 to 18 rnm long, mahogany, brown, smooth surface, and rounded both anteriorily and posteriorly.
with two taperings and parallel spines at the posterior tip. The medium sized brown moths emerge from the soil in about 2 weeks. Adult females are larger and stouter than males. Female moths live longer than males. The life cycle will be completed in little more than a month. As each female can lay more than 1000 eggs, infestations can increase very rapidly (Reed el al., 1989). More than 3000 eggs per female have been reported, though fecundity in the range of 1000 -2000 is common (Reed, 1965). In India, three species of Helicoverpa, H. armigera, H. peltigera Schiff and H.assulta Guenee have been recorded, of which H.armigera is the most H, armigera passes through four generations in Pujab. One on important.
chickpea during March, two on tomato from end of March to May, and one on maize and tomato between July to August (Singh and Singh, 1975). Bhatnagar (1980) reported seven to eight generations of H. armigera in Andhra Pradesh. Oviposition usually starts in early June, with the onset of pre-monsoon showers. Adults possibly emerge from the diapausing pupae and from the larvae on summer crops and weeds.
The pre-oviposition period range from 1 to 4 days. Oviposition period last 2 to 5 days, and post oviposition period is 1 to 2 days (Patel el. al., 1968; Singh and Singh, 1975).
by Vijayakumar and Jayaraj (1982) and found to be in descending order as pigeonpea field bean chickpea tomato cotton chillies mungbean sorghum. Reddy (1973) and Loganathan (1981) reported that pigeonpea was the preferred host for oviposition. The feeding preference descending order was pigeonpea field bean cotton sunflower sorghum chickpea mungbean urd bean and tomato. The larval period was maximum in tomato and minimum in pigeonpea and ranged from 17 to 20 days (Dhandapani and Balasubramanian, 1980).
The pupal stage ranged from 10.5 to 13.6, days being minimum on pigeonpea and maximum on sorghum, maize and sunflower.
H. armigera. It is speculated that an increase in irrigation in south lndia has led to availability of host plants throughout the dry season, and resulted in subsequent increase in pest population (Reed and Pawar, 1981). H. armigera undergoes facultative diapause during December to Febmary in North India. As a result, the pupal period lasts for more than 100 days. The prolonged pupal period leads to the low population build up during last leg of winter, season resulting in the nonavailability of larval parasitoids.
H. armigera is a multiple generation pest with a wide host range.
Therefore, the population may build up on one crop, and then move to at another in large numbers. Since the population increase may not occur within the crop, high levels of resistance are required if its populations are to be stabilized below the economic threshold level Therefore, it requires a peruse methodology to recover lines with diverse mechanisms of resistance. The ability of ovipositing females to locate and utilize a wide range of hosts from diverse plant families is one of the factors contributing to the pest status of this moth (Zalucki et al., 1986; Fitt, 1989) Learning is of fbndamental importance in understanding the host selection behaviour of H. armigera. Laboratoty evidence determining the relative preference of H. armigera for different host species does not account for the effect of experience, which can significantly alter host selection behaviour In a field situation, the
prevalence and abundance of these hosts. With the increasing resistance that H.armigera is exhibiting towards wide range of pesticides (Mc. Caffety el al., 1991). the necessity to design future pest management strategies to control this moth, becomes more apparent. Current research into the use of volatiles for monitoring and trapping, the use of trap crop and resistant crop varieties for controlling this moth all require a detailed understanding of host selection behaviour.