Effect of plant development (age and size) on the Mi-1-mediated resistance of tomato to whitefly Bemisia tabaci

Evaluation of a low-cost staining method for improved visualization of sweet potato whitefly (Bemisia tabaci) eggs on multiple crop plant species

BACKGROUND

The sweet potato whitefly (Bemisia tabaci) is a globally important insect pest that damages crops through direct feeding and by transmitting viruses. Current B. tabaci management revolves around the use of insecticides, which are economically and environmentally costly. Host plant resistance is a sustainable option to reduce the impact of whiteflies, but progress in deploying resistance in crops has been slow. A major obstacle is the high cost and low throughput of screening plants for B. tabaci resistance. Oviposition rate is a popular metric for host plant resistance to B. tabaci because it does not require tracking insect development through the entire life cycle, but accurate quantification is still limited by difficulties in observing B. tabaci eggs, which are microscopic and translucent. The goal of our study was to improve quantification of B. tabaci eggs on several important crop species: cassava, cowpea, melon, sweet potato and tomato.

RESULTS

We tested a selective staining process originally developed for leafhopper eggs: submerging the leaves in McBryde's stain (acetic acid, ethanol, 0.2% aqueous acid Fuchsin, water; 20:19:2:1) for three days, followed by clearing under heat and pressure for 15 min in clearing solution (LGW; lactic acid, glycerol, water; 17:20:23). With a less experienced individual counting the eggs, B. tabaci egg counts increased after staining across all five crops. With a more experienced counter, egg counts increased after staining on melons, tomatoes, and cowpeas. For all five crops, there was significantly greater agreement on egg counts across the two counting individuals after the staining process. The staining method worked particularly well on melon, where egg counts universally increased after staining for both counting individuals.

CONCLUSIONS

Selective staining aids visualization of B. tabaci eggs across multiple crop plants, particularly species where leaf morphological features obscure eggs, such as melons and tomatoes. This method is broadly applicable to research questions requiring accurate quantification of B. tabaci eggs, including phenotyping for B. tabaci resistance.

Plant resistance against whitefly and its engineering

Plants face constant threats from insect herbivores, which limit plant distribution and abundance in nature and crop productivity in agricultural ecosystems. In recent decades, the whitefly Bemisia tabaci, a group of phloem-feeding insects, has emerged as pests of global significance. In this article, we summarize current knowledge on plant defenses against whitefly and approaches to engineer plant resistance to whitefly. Physically, plants deploy trichome and acylsugar-based strategies to restrain nutrient extraction by whitefly. Chemically, toxic secondary metabolites such as terpenoids confer resistance against whitefly in plants. Moreover, the jasmonate (JA) signaling pathway seems to be the major regulator of whitefly resistance in many plants. We next review advances in interfering with whitefly-plant interface by engineering of plant resistance using conventional and biotechnology-based breeding. These breeding programs have yielded many plant lines with high resistance against whitefly, which hold promises for whitefly control in the field. Finally, we conclude with an outlook on several issues of particular relevance to the nature and engineering of plant resistance against whitefly.

Hsp90 Gene Is Required for Mi-1-Mediated Resistance of Tomato to the Whitefly Bemisia tabaci

The Mi-1 gene of tomato (Solanum lycopersicum) confers resistance against some nematodes and insects, but the resistance mechanisms differ depending on the harmful organism, as a hypersensitive reaction (HR) occurs only in the case of nematodes. The gene Rme1 is required for Mi-1-mediated resistance to nematodes, aphids, and whiteflies, and several additional proteins also play a role in this resistance. Among them, the involvement of the chaperone HSP90 has been demonstrated in Mi-1-mediated resistance for aphids and nematodes, but not for whiteflies. In this work, we studied the implication of the Hsp90 gene in the Mi-1 resistance against the whitefly Bemisia tabaci by means of Tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS). The silencing of the Hsp90 gene in tomato Motelle plants carrying the Mi-1 gene resulted in a decrease in resistance to whiteflies, as oviposition values were significantly higher than those on non-silenced plants. This decrease in resistance was equivalent to that caused by the silencing of the Mi-1 gene itself. Infiltration with the control TRV vector did not alter Mi-1 mediated resistance to B. tabaci. Similar to the Mi-1 gene, silencing of Hsp90-1 occurs partially, as silenced plants showed a significant but not complete suppression of gene expression. Thus, our results demonstrate the requirement of Hsp90 in the Mi-1-mediated resistance to B. tabaci and reinforce the hypothesis of a common model for this resistance to nematodes and insects.

The relationship between the infestation of Whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) and the chlorophyll content in different Eggplant varieties

The sweet potato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), is one of the most important pests in vegetables. Although the host plant Solanum melongena, is considered the most preferred, the whiteflies have preferences for particular varieties of eggplant. In this study, we evaluated three eggplant varieties in choice feeding tests. We found that the varieties of Zomorrod and Barcelona were the most preferred with the highest numbers of whitefly nymphs, which were 312 and 300 per leaf, respectively, on the last week of May. In comparison, the nymph average was 171.8 per leaf on the last week of May on the kareema. Chlorophyll concentration has been negatively affected by the infestation of B. tabaci. The investigation of the chlorophyll content ratio between the uninfested and infested eggplant leaves showed a decrease in chlorophyll content at 13.95 and 6.60 11 mg/L of the Zumorrod variety for the uninfested and infested leaves, respectively, with 52.67% chlorophyll reduction. At the same time, the mean chlorophyll content for uninfested and infested eggplant leaves of the Barcelona variety was 12.74 and 4.95 mg/L, respectively, with 61.14% chlorophyll reduction. At the same time, the Kareema variety was recorded at 17.49 and 4.95 mg/L for the uninfested and infested leaves, respectively, with 72.39% chlorophyll reduction. Furthermore, feeding by B. tabaci reduced leaf photosynthesis in eggplant by restricting gas exchange through stomata and reducing chlorophyll's content and photosynthetic capacity. Keywords: population density; piercing pest; Bemisia tabaci; Solanum melongena; host preference; plant pigments

Bemisia tabaci (Hemiptera: Aleyrodidae): What Relationships with and Morpho-Physiological Effects on the Plants It Develops on?

Although many crops have developed several adaptation mechanisms that allow them to defend against limiting factors, some biotic and abiotic stresses may cause reversible or irreversible changes in plants. Among the biotic stresses, the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is probably one of the main important pests that negatively affect several vegetable crops that are grown in greenhouses. The present study evaluated its impact on the morphology and physiology of two solanaceous plants, i.e., tomato (Solanum lycopersicum L.) and eggplant (S. melongena L.), under laboratory conditions. The results showed that, for tomatoes, plant height, shoot dry weight, leaf area, and indirect chlorophyll content were strongly reduced in infested plants, compared to the uninfested control, by 39.36%, 32.37%, 61.01%, and 37.85%, respectively. The same has been shown for eggplant, although the reduction percentages of plant height, root dry weight, and indirect chlorophyll content were less marked (i.e., 16.15%, 31.65%, and 11.39%, respectively). These results could represent interesting information for a better understanding of the B. tabaci influence on plant growth, as well as for the development of management strategies to successfully control its infestations in a cropping system.

Basal differences in the transcriptional profiles of tomato leaves associated with the presence/absence of the resistance gene Mi-1 and changes in these differences after infestation by the whitefly Bemisia tabaci

The tomato Mi-1 gene mediates plant resistance to whitefly Bemisia tabaci, nematodes, and aphids. Other genes are also required for this resistance, and a model of interaction between the proteins encoded by these genes was proposed. Microarray analyses were used previously to identify genes involved in plant resistance to pests or pathogens, but scarcely in resistance to insects. In the present work, the GeneChip™ Tomato Genome Array (Affymetrix®) was used to compare the transcriptional profiles of Motelle (bearing Mi-1) and Moneymaker (lacking Mi-1) cultivars, both before and after B. tabaci infestation. Ten transcripts were expressed at least twofold in uninfested Motelle than in Moneymaker, while other eight were expressed half or less. After whitefly infestation, differences between cultivars increased to 14 transcripts expressed more in Motelle than in Moneymaker and 14 transcripts less expressed. Half of these transcripts showed no differential expression before infestation. These results show the baseline differences in the tomato transcriptomic profile associated with the presence or absence of the Mi-1 gene and provide us with valuable information on candidate genes to intervene in either compatible or incompatible tomato-whitefly interactions.