​Screening of Pigeonpea Varieties through Nylon Bag No-choice Bioassay for Host Plant Resistance to Helicoverpa armigera

Background: The legume pod borer, Helicoverpa armigera (Hübner), is one of the most damaging crop pests, including pigeonpea. Host plant resistance is a component of pest management and therefore, we standardize a nylon bag No-Choice Bioassay technique to screen for resistance to H. armigera under field conditions. Methods: Pigeonpea plants were infested with 24 h old 1, 2, 3, 4 and 5 larvae per plant inside the nylon bag. Observations were recorded on pod damage, larval survival, larval weight, pupation, adult emergence, and fecundity after 10 days. Result: Pigeonpea varieties AL-201, H03-41 and PAU-881 exhibited lower pod damage (15.89 to 19.77%) and larval weight (12.02 to 13.82 mg). The expression of resistance to H. armigera was associated with trichome density, pod wall thickness and higher amount of phenolic compounds and condensed tannins. Lower trichome density and thin pod walls and higher amounts of sugars rendered the varieties Paras, Manak and Pussa-992 more susceptible to H. armigera. Nylon bag assay can be used to screen and select pigeonpea cultivars for resistance to H. armigera.

AaCycTL Regulates Cuticle and Trichome Development in Arabidopsis and Artemisia annua L.

Artemisinin is an important drug for resistance against malaria. Artemisinin is derived from the glandular trichome of leaves, stems, or buds of the Chinese traditional herb Artemisia annua. Increasing the trichome density may enhance the artemisinin content of A. annua. It has been proven that cyclins are involved in the development of trichomes in tomato, Arabidopsis, and tobacco, but it is unclear whether the cyclins in A. annua influence trichome development. In this study, we showed that AaCycTL may regulate trichome development and affect the content of artemisinin. We cloned AaCycTL and found that it has the same expression files as the artemisinin biosynthesis pathway gene. We overexpressed AaCycTL in Arabidopsis, and the results indicated that AaCycTL changed the wax coverage on the surface of Arabidopsis leaves. The trichome density decreased as well. Using yeast two-hybrid and BiFC assays, we show that AaCycTL can interact with AaTAR1. Moreover, we overexpressed AaCycTL in A. annua and found that the expression of AaCycTL was increased to 82–195%. Changes in wax coverage on the surface of transgenic A. annua leaves or stems were found as well. We identified the expression of the artemisinin biosynthesis pathway genes ADS, CYP71AV1, and ALDH1 has decreased to 88–98%, 76–97%, and 82–97% in the AaCycTL-overexpressing A. annua lines, respectively. Furthermore, we found reduced the content of artemisinin. In agreement, overexpression of AaCycTL in A. annua or Arabidopsis may alter waxy loading, change the initiation of trichomes and downregulate trichome density. Altogether, AaCycTL mediates trichome development in A. annua and thus may serve to regulate trichome density and be used for artemisinin biosynthesis.

Leaf Anatomical Study of Solanum Species (Solanaceae) in Iran

Solanum (Solanaceae) comprises cultivated and wild plants with 1400 species in the world and 14 species in Iran. Solanum is a taxonomically complex genus due to morphological similarities, phenotypic plasticity and hybridisation. Limited studies were done on anatomical features of this important genus. In this project, 10 native and exotic species of Solanum in Iran belonging to two subgenera were examined anatomically. Leaf mesophyll and midrib and indumentum were analysed using light microscope. Hand-made cross section method and Toluidine blue as colouring agent were used. Characters as length and width of main vascular bundle, thickness of collenchyma, trichome density, thickness of parenchyma strand, thickness of lamina and length and shape of midrib were diagnostic features among species studied. In UPGMA tree and PCA ordination, species of two subgenera were separated from each other. Results of this study confirmed the taxonomic importance of anatomical characters in Solanum species studied.

Morphological and Biochemical Constituents Influencing Aphids and Whiteflies Tolerance in Tomato Genotypes

Effects of morphological and biochemical constituents on the population of sucking insect pests infesting tomato plant were evaluated. Among the twenty genotypes evaluated under field condition at different seasons (summer, kharif, rabi), it revealed that the genotypes namely BRDT-1, EC 620421, Solanum peruvianum, EC 538455 and S. cheesmaniae had minimum number of aphid and whitefly population throughout all the three seasons due to their morphological traits like more trichome density and thick stem diameter as well as the presence of biochemical attributes like phenol and tannins which were present in those genotypes at higher concentration. The higher content of leaf chlorophyll had resistance effect against the population of aphid and whitefly, while total sugar content did not have any significant effect on resistance. Bangladesh J. Bot. 50(3): 483-489, 2021 (September)

Relationship between Soybean Pod Morphological Characteristics with Population and Attack Intensity of Pod Sucking Pest Riptortus linearis F. (Hemiptera: Alydidae)

Pod sucking pest, Riptortus linearis, is one of the important pests on soybeans which cause high yield losses. This study aimed to determine the relationship between soybean pod morphological characteristics with population and attacking intensity of the pod sucking pest R. linearis. The research method used was descriptive exploratory in the field with five soybean varieties, namely: Detap-1 (V1), Dega-1 (V2), Anjasmoro (V3), Biosoy (V4), and Dena-1 (V5). Research was conducted from September to December 2020 in Setanggor Village, West Praya District, Central Lombok Regency, West Nusa Tenggara Province, Indonesia. Results showed that the highest population of R. linearis was in the Dena-1 variety (1.9 individuals/plant), followed by Detap-1 (1.7 individuals/plant), Anjasmoro (1.6 individuals/plant), Dega (1 individual/plant) and Biosoy (0.9 individual/plant). Two morphological characteristics of soybean pods that had a correlation with the attacking intensity of R. linearis were trichome density (TD) and trichome length (TL). The lowest attacking intensity was on Biosoy variety (26.08% b, TD:1000.7 (10,000 m2 (10 x 4) and TL: 71.78 µm followed by Dega-1 (27.98% ab, TD:1044.04 (10,000 m2) (10 x 4) and TL: 70.70 µm, Detap-1 (36.36% ab TD: 944.14 (10,000 m2 (10 x 4) and TL: 72.86 µm, Dena-1 (35.02 % ab TD: 957.55 (10,000 m2 (10 x 4) and TL: 73.11 µm and the highest is Anjasmoro (37.56% a TD: 955.24 (10,000 m2 (10 x 4) and TL: 74.67 µm. Furthermore, the correlation analysis showed that the denser and longer the pod trichomes, the lower the attacking intensity of the pod sucking pest R. linearis.

Hair (H) interacts with SlZFP8-like to regulate the initiation and elongation of trichomes by modulating SlZFP6 expression in tomato

Trichomes are specialized glandular or non-glandular structures that provide physical or chemical protection against insect and pathogens attack. Trichomes in Arabidopsis, as typical non-glandular structures, have been extensively studied. However, the molecular mechanism underlying glandular trichome formation and elongation still remains largely unknown. We previously demonstrated that Hair (H) is essential for the formation of type I and type VI trichomes. Here, we found that overexpression of H increased the density and length of tomato trichomes. We revealed that H physically interacts with its close homolog SlZFP8-like (SlZFP8L) and SlZFP8L also directly interacts with Woolly (Wo) by biochemical assays. SlZFP8L overexpression plants showed increased trichome density and length. We further found that the expression of SlZFP6, encoding a C2H2 zinc finger protein, is positively regulated by H. We identified that SlZFP6, is a direct target of H through ChIP-qPCR, Y1H, and LUC assays. Similar to H and SlZFP8L, the overexpression of SlZFP6 also increased the density and length of tomato trichomes. Taken together, our results suggest that H interacts with SlZFP8-like to regulate the initiation and elongation of trichomes by modulating SlZFP6 expression in tomato.

Chronic Gamma Irradiation Changes Phenotype and Gene Expression Partially Transmitted to Next-Generation Tomato Seedlings

Compared to the studies on acute irradiation of seeds, fewer studies have reported on the chronic irradiation of seedlings, especially in fruit-bearing vegetables. We examined the effects of chronic gamma irradiation on tomato (Solanum lycopersicum ‘Micro-Tom’) seedlings exposed to gamma rays (50, 100, 150, and 200 Gy) for 4 weeks. As the total dose of gamma rays increased, leaf length, trichome density, and seed number were reduced in the irradiated seedlings (M1). Additionally, a change in fruit shape was observed. Chronic gamma irradiation reduced the expression of two trichome-related genes and affected the expression levels of 11 reactive oxygen species (ROS)-related genes. We examined the transmittance of these effects using M2 plants. The trichome density and fruit shape were similar between M2 and control plants; however, a reduction in leaf length and seed number was detected in M2 plants. Interestingly, changes in the expression of four ROS-related genes (ZAT10, Mn-SOD, POD3, and RBOH1) found in M1 were detected in M2 plants. Thus, the changes in phenotype and gene expression induced by chronic gamma irradiation were transmitted to the next generation. Additionally, we found novel mutants from M2 plants, suggesting that chronic gamma irradiation may be considered in tomato mutation breeding.

↵​Study of Morpho-physiological and Biochemical Traits for Resistance to Yellow Mosaic Virus (YMV) in Blackgram [Vigna mungo (L.) Hepper] Varieties

Background: Blackgram is one of the most important pulse crop in India and it is being affected by a number of insect pests from seedling stage to maturity. Among them whitefly is an important insect pest that transmit the viral disease, yellow mosaic virus (YMV), which is a major disease resulting in severe yield losses accounting for about 70% and infection at early stages may result in complete failure of the crop causing huge loss to the farmers economically. To overcome the losses due to this important disease in blackgram, study of host plant resistance to whiteflies, thereby minimizing the losses due to YMV disease is of great importance. The trichome density plays an important role as a morphological anti-feedant which reduces the pest attack and subsequently lowers the disease incidence and the plants with high trichome density showed less YMV symptom. The morpho-physiological and biochemical traits play an important role in host plant resistance against YMV disease through insect vector resistance and hence, the study was undertaken. Mathods: A field experiment was conducted during rabi 2017-18 and 2018-19 at RARS, Lam, Guntur in a randomized block design with eight blackgram varieties and replicated thrice under receding soil moisture condition. The experiment was conducted using eight blackgram varieties (LBG 787, GBG 1, TBG 104, LBG 884, LBG 806, LBG 808, LBG 623 and LBG 752) obtained from RARS Lam, Guntur and the variety LBG 623 was considered as a susceptible check. The estimation of sugars, phenols, tannins, trichome density and SCMR was done at vegetative and reproductive stages of crop growth. Result: A significant variation was observed among the varieties for all the traits observed at vegetative and reproductive growth stages during both rabi 2017-18 and 2018-19. The total sugar content of the blackgram varieties varied from 25.16 to 49.82 mgg-1 FW; the leaf phenolic content values ranged from 10.26 to 23.55 mg g-1 FW and the tannins content of the dried leaf samples ranged from 0.014 to 0.052 mgg-1 DW. The trichome density of the blackgram varieties varied from 12.91 to 74.59/cm2 of leaf area and the SCMR values ranged from 24.21 to 55.17. Higher seed yield was recorded in the variety LBG 884 followed by GBG1 and the lower seed yield was recorded in the variety LBG 623 during rabi 2017-18 and 2018-19. The YMV resistant varieties showed relatively higher phenolic, tannins content and trichome density and lower total sugar content in the leaf. The total sugar content showed a significant negative correlation with the seed yield. The SCMR value was significantly lower in the susceptible varieties of blackgram with higher disease scores.

Squash Varieties Domesticated for Different Purposes Differ in Chemical and Physical Defense Against Leaf and Root Herbivores

Plant domestication often reduces plant defenses by selection on chemical and physical defense traits. Thus, it is expected that herbivorous insects perform better on crop varieties than on their wild relatives. However, recent studies show that this pattern is not ubiquitous. We examined how varieties of squash (Cucurbita spp.) domesticated for different purposes (for consumption or as ornamentals), differ in plant defense traits and in their interactions with a leaf and a root herbivore. Two types of defenses were measured: cucurbitacins, which are toxic phytochemicals, and trichomes that are physical barriers for most herbivores. We addressed the following questions: (i) what is the variation in cucurbitacin content and leaf trichome density among varieties? (ii) does purpose of domestication explain differences in defense traits among varieties? and (iii) are herbivore feeding preferences and performance altered by the defense traits of squash varieties? We found great variation in cucurbitacin content among varieties, but not according to their purpose of domestication. Cucurbitacins were found mostly in cotyledons and roots and in very small quantities in the leaves. In contrast, trichome density was greater on the varieties selected for consumption than on the ornamental varieties. The performance of a leaf herbivore (Spodoptera latifascia) and a root herbivore (Diabrotica balteata), was not different among squash varieties. Moreover, in a choice experiment, larvae of the root herbivore preferred to feed on squash varieties with high cucurbitacin content. Whereas, in the field, native leaf herbivores preferred to feed on varieties selected for consumption. Our results contribute to a better understanding on how varietal selection may differentially affect plant defenses. This knowledge could help in the development of crop varieties with enhanced insect resistance.