Screening of mustard varieties against sucking insect pests of mustard

The experiment was conducted at Mustard Oil Field, Agriculture Research Jaffarabad Seed Farm Usta Muhammad, Balochistan in a RCBD design with three replications to monitor the population dynamics of sucking insect pests on mustard.Five mustard varieties i.e. UCD-1202, NMT-8, Canola, Nawab Shah and P-25 was screened to evaluate the relative resistance against sucking insect pests. The monitoring of the sucking insect pests was started right from 15 December, 2018 to 06 March, 2019. The population buildup of each sucking insect pest was monitored at weekly interval. Highest infestation of whitefly (0.98±0.29 nymphs per plant) was recorded for Nawab Shah followed by P-25 (0.92±0.26 nymphs per plant), NMT-8 (0.89±0.25nymphs per plant) and Canola (0.82±0.22 nymphs per plant), while lowest infestation (0.77±0.21 nymphs per plant) was observed for UCD-1202. Highest infestation of thrip (3.20±0.78 nymphs per plant) was recorded for Nawab Shah followed by P-25 (3.08±0.75 nymphs per plant), NMT-8 (2.97±0.70 nymphs per plant) and Canola (2.93±0.6 nymphs per plant), while lowest infestation (2.50±0.57 nymphs per plant) was observed for UCD-1202. Overall mean highest population of jassid (0.74±0.20nymphs per plant) was recorded for Nawab Shah followed by P-25 (0.60±0.30 nymphs per plant), Canola (0.59±0.15 nymphs per plant) and NMT-8 (0.56±0.16nymphs per plant), while lowest infestation (0.19±0.05 nymphs per plant) was observed for UCD-1202. Highest infestation aphid (21.80±10.28 nymphs per plant) was recorded for Nawab Shah followed by P-25 (20.78±10.10 nymphs per plant), NMT-8 (20.48±9.64 nymphs per plant) and Canola (18.85±9.07nymphs per plant), while lowest infestation (18.27±9.04 nymphs per plant) was observed for UCD-1202.


Introduction
Rapeseed (Brassica spp.) is grown primarily for its seed which yields about forty percent oil and a high-protein animal feed. The scientists have sequenced the entire genome of rapeseed/canola (Brassica napus) and its constituent genomes present in Brassica rapa and Brassica oleracea in 2009 [1]. Brassica napus (canola) is covered with more bloom than other species. It is very late in maturity and remains green untill about the middle of April. Canola has been especially developed for oil by the Canadian scientists. They have tried to reduce the amount of erucic acid in this newly bred variety. Canola oil is the lowest in saturated fat, containing only 6% saturated fat and is high in mono-saturated fat. This has 50% less saturated fat than corn oil [2]. The attack by insect pests and diseases are one of the key factors result of low yield. The mustard crop is more vulnerable to a extensive variety of insect pests from sowing till harvest than other oil seed crops. The insect pests of economic importance are, cabbage aphid, Brevicoryne brassica (L), mustard aphid, Lipaphis erysimi (Kalt.), mustard sawfly, Athalia proxima (Klug), cabbage butterfly, Pieris brassicae (Linn), Painted bug Bagrada picta (K), Mustard leaf eater, Spodaptera litura (F), leafminer, Chromatomyia horticola (Goureau) Thrip, Thrip tabaci and Whitefly, Bemesia tabaci (Gennedius) [3]. These insect-pests can be grouped as key pest, major pest and minor pest on the basis of their economic importance. The infestation of sucking insect pests (white fly, thrips, jassid and aphid) is one of the main factors responsible for less yield of mustard. The mustard crop is highly vulnerable to a wide variety of insect pests from sowing till harvest than other oil seed crops [3]. The whiteflies are a limiting factor in the yield of mustard and rape seed. Whitefly (Bemisia tabaci Genn.) is small insect having four white membranous wings. The nymphs are oval and light yellow in colour and remain in clusters on the under surface of leaves. It breeds all the year, the eggs hatch in 3-6 days. Whitefly eggs are generally laid on the underside of leaves. The newly laid eggs are yellow/green, changing color to dark tan, as they are about to hatch. They are very small, oval shaped, and sit on top of a pedicel (stalk) that fits into a small slit in the leaf made by the female.  [9] reported that most of the hybrid mustard cultivars with thicker stems were resistant to L. erysimi and mustard sawfly. Sahito et al. [10] indicated that white fly B. tabaci, (Genn). mustard aphid L. erysimi (Kalt) and Bagrada picta (F) were major mustard insect pests and Their population buildup was higher recorded on variety Yellow sarsoon 'Brown sarsoon' Das et al. [11] showed that relative humidity and rainfall had negative influence on pests and natural enemies during the study period. Bhati et al. [12] examined varietal resistance in rape-seed mustard and reported that mustard aphid, mustard sawfly, painted bug and cabbage butterfly were found attacking the mustard crop; while varieties BSH-1 and YST-151 showed higher susceptibility to mustard aphids as compared with brassica varieties Narendra Rai, GSC-6 and T-27. Singh et al.
[8] reported that on variety YST-151 the aphid population was 2.9 larvae/10 plants showing susceptibility to sawfly. The proposed study is mainly aimed at evaluating the varietal resistance of mustard against sucking insect pests under field conditions.

Materials and methods Experimental area
The experiment was conducted at Mustard Oil Field, Agriculture Research Jaffrabad Seed Farm Usta Muhammad, Balochistan.

Experimental design
The experiment was laid out in a Randomized Complete Block Design (RCBD) having net plot size of 5 x 1.2 m with three replications to monitor the population dynamics of sucking insect pests on mustard.

Selection of mustard cultivars
Five mustard varieties i.e. UCD-1202, NMT-8, Canola, Nawab Shah and P-25 and was screened to evaluate the relative resistance against sucking insect pests.

Monitoring and data collection
The monitoring of the sucking insect pests was started right from 15 th December, 2018 to 06 th March, 2019. The population buildup of each sucking insect pest was monitored at weekly interval. The observations regarding the sucking insect pest population was noted on the basis of randomly selected five plants from top, middle and bottom for each mustard variety. The sucking insect pests were identified and recorded their population in separate data recording sheets weekly.

Data analysis
Data was analysed using descriptive statistics (Statistix ver. 8.1). The significance of the differences in population level of the insect pests was evaluated using analysis of variance and least significant difference test.    Crop Yield (kg ha -1 ) Results in regards to crop yield is presented in (Fig. 1). Statistical analysis of the obtained data indicated that there was significant difference in crop yield between all the five mustard varieties. On the basis of average, the maximum crop yield (1850.53 kg plot -1 ) was recorded for UCD-1202 followed by NMT-8 (1560.2 kg plot -1 ), P-25 (1540.5 kg plot -1 ) and Canola (1520.3 kg plot -1 ) and the minimum crop yield (1498.8 kg ha -1 ) was noted for Nawab Shah mustard variety.

Discussion
The infestation of sucking insect pests (white fly, thrips, jassid and aphid) is one of the important factors responsible for below yield of mustard. The mustard crop is more vulnerable to a wide variety of insect pests from sowing till harvest compared to other oil seed crops [3]. The research is carried out worldwide to examine the varietal resistance and management of the sucking complex on oilseed crops. The findings of the study indicated that highest whitefly population was recorded on Nawab Shah Variety and the lowest whitefly population was recorded on variety UCD-1202. The LSD test suggested that the differences in whitefly population among mustard varieties were statistically significant (P<0.05). These results are further supported by Rohilla et al.
[5] who reported that whitefly population varied significantly among mustard varieties; while Bhatti and Soomro [13] showed that mustard varieties with tricons showed resistance to whitefly; while varieties having leaves without tricons suffered with more infestation of sucking insect pests. In another study, Panda and Khush [6] observed that development of mustard varieties resistant to sucking complex could increase the seed yield manifold; while Rangrez et al. [14] reported varied response of mustard varieties to whitefly infestation. The crop varieties play significant role in insect pest infestation; as varieties preferred by insect pests are economically harmful for the farmers. Cultivation of insect-resistant crop varieties may suppress insect pest infestation and control plant diseases transmitted by insects. If there are persistent viruses, plant resistance to their transmitters usually reduce virusspread by slowing down their replication [6]. If pest resistant varieties are used with chemical control methods, the costs of chemical control and problems related to insecticides may be reduced [15].
Consequently, the use of resistant plant varieties plays an important role in reducing environmental pollution. There are several factors that make resistant plants inappropriate host plant species for pests [16]. Different parts of a plant, the leaf age and the hairy leaves are effective for feeding and egg laying, selection and changes in the B. tabaci populations on rapeseed-mustard [1]. Fuzz and fluffs can be a physical barrier and also provide a suitable microclimate for vegetarians [17]. There are several defense mechanisms against pests, such as: the number and type of trichoms [18], and chemicals substances as well as the pod thickness [12]. Leidl et al. [19] examined varietal resistance in rape-seed mustard and reported that mustard aphid, mustard sawfly, painted bug and cabbage butterfly were found attacking the mustard crop; while varieties BSH-1 and YST-151 showed higher susceptibility to mustard aphids as compared with brassica varieties Narendra Rai, GSC-6 and T-27. Singh et al.
[8] reported that on variety YST-151 the aphid population was 2.9 larvae/10 plants showing susceptibility to sawfly. Sahito et al. [10] indicated that Bemisia tabaci, (Genn). was one of themajor mustard insect pests and showed that higher (6.71+0.98/leaf) population of B. tabaci was recorded on Yellow sarsoon than Dark green leaves (6.30 + 0.61), Brown sarsoon (6.19 + 0.63), Raya Anmol (5.40 + 0.55), Torya Early (5.38+0.57) and Rai S-9 (3.79+0.50). Das et al. [11] showed that relative humidity and rainfall had negative influence on pests and natural enemies during the study period. The study showed that the thrips population was highest on variety Nawab Shah variety and lowest thrips population was observed on UCD-1202 variety. This indicates that variety 'UCD-1202' showed higher relative resistance to thrips when compared with rest of the varieties. The LSD test indicated that the differences in thrips population among mustard varieties were statistically  [23] argued that mustard varieties with rsistance against sucking complex, particularly jassid is of great economic importance. The study showed that the jassid population was highest on variety Nawab Shah variety and lowest jassid population was observed on UCD-1202 variety. This indicates that variety 'UCD-1202' showed higher relative resistance to jassid when compared with rest of the varieties. The LSD test indicated that the differences in jassid population among mustard varieties were statistically significant (P<0.05). Panda and Khush [6] found that jassid population on mustard varieties with thicker stems was lower than thin stemmed varieties. Verma et al.
[3] experienced a great variation in the jassid population among different mustard cultivars. Malik et al. [23] argued that mustard varieties with rsistance against sucking complex, particularly jassid is of great economic importance. The findings of the study indicated that highest aphid population was recorded on Nawab Shah variety and the lowest aphid population was recorded on variety UCD-1202. The LSD test suggested that the differences in aphid population among mustard varieties were statistically significant (P<0.05). The sucking insect pest resistance trend suggested that UCD-1202 may preferably be cultivated having some resistance to sucking insect pests. These results are in accordance with those of Rohilla et al. found that varieties with thicker pods suppressed insect pest infestation and showed resistance in diseases transmitted by insects; while Karmakar [24] compared mustard cultivars B-9, NC-1, RW-351 and PGS-1004 for resistance to Lipaphis erysimi and found that lowest aphid population was recorded on PGS-1004 and this cultivar also showed higher yield than rest of the cultivars. Singh et al.
[8] reported that Indian mustard (cv. Pusa Jai Kisan) showed relative resistance to Lipaphis erysimi; while Saljoqi et al. [25] reported that most of the hybrid mustard cultivars with thicker stems were resistant to Lipaphis erysimi and mustard sawfly. Sahito et al. [10] indicated that Lipaphis erysimi (Kalt) was the major mustard insect pest and showed that higher aphid population was noted on Yellow sarsoon than Dark green leaves, Brown sarsoon, Raya Anmol, Torya Early and Rai S-9. Das et al. [11] showed that environmental factors had also significant impact on the insect pest population.

Conclusion
It is concluded that maximum infestation of whitefly, thrip, jassid and aphid was observed for variety 'Nawab Shah' and minimum was observed for variety 'UCD-1202'. The peak infestation of the sucking complex was observed in the month of January in all five mustard varieties.