Browsing by Author "Parajulee, Megha N."
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Item Breeding value and utilization of host plant resistance for integrated thrips (Thysanoptera: Thripidae) management in cotton (Gossypium spp.)(2015-05) Wann, Dylan Quincy; Dever, Jane G. K.; Hequet, Eric F.; Parajulee, Megha N.; Pepper, Kelly; Rock, Christopher D.; Wright, Robert J.Thrips are common early-season pests in cotton systems across the U.S. Host plant resistance, as part of an integrated management strategy, could be a critical tool for reducing thrips damage to cotton in both conventional and organic systems. Also, identifying and developing viable, non-transgenic cotton genotypes for organic cotton production would be valuable for growers desiring new, high-quality cultivars for their production systems. Field and greenhouse trials were conducted in 2011-2014 at the Texas A&M AgriLife Research and Extension Center at Lubbock, and at a number of cooperators’ farms on the Texas High Plains, to evaluate twenty-two cotton genotypes for novel thrips resistance and agronomic potential for organic production. Three G. hirsutum breeding lines, 07-7-519CT, 07-7-1020CT, and 11-2-802GD, exhibited the greatest resistance to thrips damage and had the greatest overall potential for utilization in organic production. Field and greenhouse trials were also conducted in 2011-2013 to elucidate the overall breeding value of thrips resistance. Broad sense heritability ranged 41-67%, depending on the family. H2 was higher in families with a day-neutral resistant parent than those with a photoperiodic resistant parent. Observed segregation ratios fit 3:1, 13:3, and 11:5 expected resistant/susceptible ratios, depending on the family. These results indicate that thrips resistance is a simply-inherited dominant trait, likely controlled by one or two genes. Actual gain from selection ranged 2-21% per cycle of selection, depending on the selection intensity. The optimum selection intensity in these evaluations was 5%, resulting in an approximate 21% gain. Field trials were also conducted in 2013-2014 to evaluate the combination of partially-resistant advanced breeding lines with weekly spray applications of spinosad insecticide on thrips populations and subsequent damage to a cotton crop. Resistant genotypes resulted in 26-37% reductions in thrips injury over the controls. In addition, spinosad applications alone reduced thrips injury up to 37% and increased lint yield 10% in 2013. However, these results were not consistent between 2013 and 2014, as a result of low thrips populations in 2014 and minimal subsequent damage to the crop. Overall, these evaluations revealed that host plant thrips resistance varies widely in cotton and can be sufficiently captured and introgressed by plant breeders. Resistant germplasm is also an effective tool for the integrated management of thrips pests and their damage to a cotton crop.Item Characterization and assessment of an iridoviral-kinase gene (ISTK) and its subfragment (iridoptin) as plant-incorporated protectants against aphids(2015-08) Ganapathy, Saranya; Bilimoria, Shan L.; Zhang, Hong; Parajulee, Megha N.; San Francisco, Michael; San Francisco, Susan; Payton, Paxton R.Insect pests are a key factor in reduction of agricultural productivity. The economic impact of insect pests exceeds $200 billion globally and is $33 billion for the U.S. Extensive use of chemical insecticides is dominating other insect control strategies. Development of insecticide resistance in more than 600 insect pest species has demanded higher doses with consequent environmental damage, pest resurgence, and lethal effects on non-target species. Use of genetically-modified (GM) crops offers a promising alternative. Insect-resistant GM crops commercialized thus far utilize insecticidal-Bacillus thuringiensis (Bt) δ-endotoxin genes and confer resistance to lepidopteran and coleopteran pests. However, pest resistance due to prolonged and over-use of Bt toxins is becoming an issue, and phloem-feeding insect pests (such as aphids) are not susceptible to Bt crops. Thus, new polypeptide toxins working through novel mechanism must be identified to overcome resistance and targeting issues with Bt toxins. Our research group has been exploring insect viruses for the identification of potential plant-incorporated protectants (PIPs) for pest control. Earlier studies have shown that Chilo iridescent virus (CIV, family Iridoviridae) induces mortality and metamorphic deformity in the cotton boll weevil, reduces aphid populations, but does not infect mammalian cells. A CIV gene responsible for this insecticidal activity has been identified in our lab and has been designated iridovirus serine/threonine kinase (ISTK). A 35-kDa cleavage product (designated iridoptin) of the 48-kDa ISTK polypeptide induces apoptotic blebbing (programmed cell death) and host protein shutoff in insect cells and causes 50% and 100% mortality in cotton aphids and green peach aphids, respectively. This is the first iridovirus-encoded kinase shown to induce apoptosis in insect cells and probably works through novel mechanism. The goal of this research was to assess the potential of transgenic plants expressing ISTK/iridoptin in aphid control. In this research, initial efforts to transform and express the native-iridoptin gene fragment in model plant, Arabidopsis, yielded gene-specific RNA but not protein. Therefore, the viral gene and its subfragment, ISTK and iridoptin, were modified and codon-optimized for its efficient expression in plant system. Codon-optimized gene constructs resulted in significant improvement in the levels of accumulation of the insecticidal toxins, ISTK and iridoptin, using transient-expression system in tobacco. Later, an optimized-transient expression platform was established for ISTK/iridoptin in tobacco, which would serve as a valuable-assessment tool for testing the range of agricultural insect pests that can be controlled using these plant-expressed toxins. Efficacy of ISTK/iridoptin for aphid control was examined by creating stable, transgenic Arabidopsis plants. Plant-expressed ISTK and iridoptin (at T1 generation) severely inhibited the survival of green peach aphids (GPAs; with up to 100% mortality) and significantly suppressed the fecundity of surviving aphids in excised-leaf bioassays. However, a concentration-dependent effect of the plant-expressed toxin on GPAs was not observed. These results would still serve as a proof-of-concept data and shed light on the utility of these aphicidal toxins when expressed in plants. This represents a progressive step forward in understanding and maximizing the potential of this novel, insecticidal iridovirus kinase as a PIP. However, more detailed analyses are needed in order to closely study the inheritance of this toxin’s expression and insecticidal activity in multiple transgenic generations, and possible adverse effects on non-target organisms. The specificity of ISTK/iridoptin can make it an attractive alternative to chemical pesticides, Bt, and other insecticidal toxins, provided the stability and efficacy of these toxins can be demonstrated in planta. This dissertation generated the first report of utilizing an iridovirus kinase towards development of aphid-resistant transgenic plants. This creates a new niche for identification and exploration of similar toxins, as aphid control agents, that are of potential agronomic interest. Hence, this study would serve as a pioneer in the use of insect viruses such as CIV for an effective and sustainable insect pest control in agriculture.Item Effect of irrigation and tillage practices on cotton fleahopper Pseudatomoscelis seriatus (Reuter) and predator activity in the Texas Rolling Plains(Texas Tech University, 2007-12) Albeldaño, Walter Alfredo; Parajulee, Megha N.; Slosser, Jeffrey E.; Segarra, EduardoField studies were conducted at Munday, Knox Co. Texas, during the years 2003 to 2005 to evaluate the effects of irrigation and tillage system on cotton fleahopper (Pseudatomoscelis seriatus Reuter) seasonal activity in cotton. Irrigation treatments included 40-inch spacing subsurface drip, 80-inch spacing subsurface drip and standard furrow irrigation. Tillage treatments were conservation and conventional tillage systems.Item Expression of the AtNHX1 gene in peanut to increase salt tolerance in peanut plants(2010-08) Banjara, Manoj; Zhang, Hong; Parajulee, Megha N.; Payton, Paxton R.Salinity and drought are two major environmental stresses that affect agricultural productivity. To meet the food demand of an increasing population and a warming environment, the need to generate salt and drought tolerant crops is apparent. High salinity in the soil makes it harder for plant roots to extract water, and high concentration of salts within plant cells can be toxic to the cellular enzymes. One approach to improve salt tolerance in crops is to sequester excess sodium ion (Na+) into the large intracellular vacuoles via the tonoplast membrane. Consequently, there is reduction of Na+ in cytoplasm with the accumulation of compatible solutes that restore the correct osmolarity to the intracellular milieu, which favors water uptake by plant root cells and improves water retention in tissues under high soil salinity. This approach was successfully demonstrated in several plants, where overexpression of the Arabidopsis gene AtNHX1 that encodes a vacuolar sodium/proton (Na+/H+) antiporter resulted in a higher salt tolerance phenotype. Peanut (Arachis hypogaea L.) is an important crop of tropical and sub-tropical regions of the world. To improve yield and quality under salinity stress conditions, the Arabidopsis gene AtNHX1 was introduced into peanut through Agrobacterium-mediated transformation. The AtNHX1-expressing peanut plants produced more biomass when grown on up to 150 mM NaCl in greenhouse conditions. The increased growth of AtNHX1-expressing peanut plants is likely due to the consequence of higher photosynthetic rates in the transgenic plants compared to wild-type plants under saline conditions. The better performance of AtNHX1-expressing peanut lines compared to wild-type plants under high salinity indicates that AtNHX1 can be used to enhance salt tolerance in peanut.Item Lygus hesperus Knight in the Texas High Plains: Cotton compensation after fruit damage and host plant selection with implications for cotton IPM(2006-12) Barman, Apurba K.; Parajulee, Megha N.; Dotray, Peter A.; Deslippe, Richard J.Texas High Plains is known for its extensive cotton cultivation in the world. Considering the importance of Lygus bug as one of the insect pests of cotton in adjoining states like Mississippi, Arkansas, Arizona and California, research effort was undertaken to generate information on behavioral and insect-host interactions. Compensation ability of cotton was evaluated under the prevailing regional growing conditions. Fruit loss due to augmentative release of Lygus bug at two levels (1 and 3 bugs/plant) was higher than control treatments. Partial yield compensation was observed when bugs were released in early-bloom stage of the crop. Besides, attractiveness of different non-cotton hosts to Lygus bug was demonstrated which may have implications in cultural control. Russian thistle and alfalfa was found be more attractive than pigweed, sunflower and Palmer amaranth. Cotton was not preferred at any of its growth stages when other hosts were present in vicinity.Item Lygus hesperus population dynamics on the selected host plants(2009-05) Chen, Chen; Parajulee, Megha N.; Trindade, A. Alexandre; Bednarz, Craig W.Laboratory studies were conducted to generate basic biological information of Lygus hesperus on alfalfa, pigweed, Russian thistle, green bean, artificial diet, cotton square and cotton boll. The nymphal development was significantly longest, almost two times longer, in the cotton boll compared to other hosts. The average nymphal development was about 15 days in other hosts except cotton boll at 27 oC. The nymphal survivorship was significantly lowest in the cotton boll. The average total nymphal survivorship was around 60% and the highest mortalities were focused on the first 3 instars. The sex ratio of the L. hesperus was not affected by the different diets. The life-table parameters were obtained in cotton square, artificial diet, green bean and alfalfa. The adult longevity in artificial diet was shortest (18.7 days) for the highest fecundity used up all the energy of the insects and the green beans had the longest longevity (36.09 days). The rm values were higher in artificial diet and green bean, and lower in cotton square and alfalfa. λ values showed the same pattern. Even though all those two parameters were significantly different in cotton square and alfalfa, those two parameters on two hosts were numerically similar. The rest two parameters GRR and Ro showed the same pattern as well. But the T and DT values showed the different pattern caused by the shortest longevity in artificial diets and longest longevity in green beans. All the study showed that cotton, especially cotton square can offer enough nutrition to let L. hesperus grow during the early summer in the field.Item Ontogenic morphometry and genetic diversity of Lygus hesperus (Hemiptera: Miridae)(2011-05) Shrestha, Ram B.; Parajulee, Megha N.; Francisco, Michael J. D. S.; Densmore, Llewellyn D.; Holaday, A. Scott; Strauss, Richard E.; Burow, Mark D.Lygus hesperus Knight (Hemiptera: Miridae) is an economically important pest of many field crops, including cotton, in the United States. Lygus hesperus is commonly found in the western United States, hence, it is commonly known as Western Tarnished Plant Bug. Lygus hesperus populations from different geographic regions respond differently to the identical pest management practices. Population-specific pest management strategy is required for successful management of this pest. Morphological or molecular techniques or biological assays could be used to differentiate these Lygus populations. But scientific information on ontogenic morphometry and genetic diversity of this species is mostly lacking. Therefore, ontogenic morphometry, and genetic diversity studies were conducted in the cotton entomology laboratory at Texas AgriLife Research Center, Lubbock, Texas. Lygus hesperus has allometric ontogenic growth patterns and there was no significant difference between ontogenic shape and size trajectories between male and female. The discriminant function analysis revealed significant differences in pattern of ontogenic shape and size between Lygus hesperus and Lygus lineolaris. Thus, the morphometric technique can be used to differentiate nymphal stages of two species when they are hard to differentiate by visual observation of their morphology. Ten polymorphic microsatellite markers were developed and used in a genetic diversity study of eight Lygus hesperus populations from the Texas High Plains. Lygus hesperus population from this region showed a high degree of genetic diversity. Lygus hesperus from the Texas high Plains showed significant genetic population structure and they were differentiated into three genetically distinct populations. The molecular marker comparison study showed Simple Sequence Repeat (SSR) and Amplified Fragment Length Polymorphism (AFLP) markers are potential markers for genetic diversity study of this species when the capillary electrophoresis facility is available but Inter Simple Sequence Repeat (ISSR) markers can be next alternative when the capillary electrophoresis facility is not available. Morphometric and molecular biology knowledge and techniques developed in these studies will be useful in identification of pest management units and development of population specific precision pest management technology for Lygus hesperus.Item Potentials and prospects of strip cropping in the management of cassava whitefly (Bemisia tabaci) in peri - urban agroecosystems(2008-08) Ewusie, Ebenezer; Parajulee, Megha N.Cassava (Manihot esculenta Crantz, Euphorbiaceae) is one of the main tuber crops that occupy an exceptionally important position as a food security commodity for smallholder farmers in sub-Saharan Africa. However, cassava mosaic virus disease (CMD) caused by cassava mosaic geminiviruses (CMGs) (Geminiviridae: Begomovirus) and transmitted by whitefly (Bemisia tabaci) threatens the production of this crop in Africa, causing an estimated annual yield loss of over 1.5 billion US dollars. Control measure to date has been the use of virus-resistant varieties, but low cost cultural control measures such as intercrops or manipulation of the cropping system have been relegated to the background. Most African farmers are unable to afford insecticides for the control of this insect while the insect has developed resistance against most classes of insecticides. This thesis examines the possibility of manipulating the cropping system using strip crops, a low cost and low input cultural control method, in managing Bemisia tabaci populations in cassava. A significantly lower number (P < 0.05) of immature (egg and nymph) and adult Bemisia tabaci were found in cassava plots surrounded on all sides by five rows of both cotton and Jatropha curcas. Additionally, J. curcas strips appeared to repel Bemisia tabaci and lower its populations in cassava. Planting of J. curcas around cassava plots also lowered CMD severity in cassava significantly. Future studies including investigations into the insecticidal and ovicidal properties of J. curcas will elucidate the behavioral and physiological mechanism for whitefly suppression in cassava.