SUSVEG-Asia Tomato IPM

Tomato Lycopersicum esculentum Mill

Family: Solanaceae

Tomato is a highly nutritive vegetable popular throughout the world and South Asia in particular. The recent introduction of hybrid varieties in India has greatly increased yields making the crop highly profitable for resource-poor farmers, although in some seasons excess production has led to a collapse of market prices. Production is essentially restricted to the winter period (November to February) because of the absence of heat tolerant varieties although this also limits the impact of insect pests, such as the fruit borer, Helicoverpa armigera which can account for up to 15% yield loss. Nevertheless, the sustainability of crop production is threatened by a complex of pest and disease constraints, most notably tomato leaf curl virus disease (ToLCVD) caused by viruses of the genus Begomovirus, family Geminiviridae, which are efficiently transmitted by the whitefly vector, Bemisia tabaci. The recent introduction of the B-type biotype of B. tabaci into Southern India resulted in severe crop losses and in response considerable research efforts have been employed to develop coping strategies to break the tri-trophic host-vector-disease cycle for the benefit of resource-poor farmers and consumers. This research has identified a number of viruses in India that produce ToLCVD symptoms and these viruses are distributed in different regions of the country. The research has also led to the development of a number of tolerant/resistant cultivars and practical methods to reduce the vector pressure on the crop.

The main thrust of the SUSVEG project was to test tolerant/resistant cultivars with the cultural methods in Tamil Nadu, Andhra Pradesh and Bangladesh and to investigate the molecular diversity of virus and vector populations in Bangladesh.

Additional activities were conducted to evaluate the efficacy of biopesticides on control of root knot nematode, Meloidogyne incognita, and develop floral attractants for trapping male and female H. armigera. The results of the latter research are discussed under country bean IPM.

Tomato leaf curl virus disease IPM

A virus-free crop is desirable but not essential. If infection occurs during the seedling stage plants become sterile and this can result in 100% loss of yield. Thus, ideally infection should be prevented during the vegetative and early flowering period (50 to 60 days after sowing) to minimise the impact of the disease on yield. This can be achieved by enclosing nurseries in netting and surrounding young transplanted plants by physical barriers to reduce exposure to B. tabaci. NRI researchers working by colleagues from the University of Agricultural sciences, Bangalore, found that light blue cloth barriers (1 m high) with a yellow strip had a significant impact of disease transmission allowing farmers to produce a viable crop.


Infested susceptible line, no fruit	Total crop loss caused by ToLCVD

Tomato nurseries protected by netting	Barrier protects young plants from B. tabaci

Reactions of different tomato genotypes to geminivirus

In order to develop resistant/tolerant tomato varieties with commercially acceptable traits wild Lycopersicon species, such as L. chilense, L. peruvianum and L. hirsutum, have been employed as sources of resistance in a global research effort. Collaborators at TNAU, CSA and BARI were provided with seed of 12 geminivirus-resistant tomato lines and one susceptible check (CLN2026D) by AVRDC. Five lines (CLN-prefixed, TLB111, H24) carried a single gene called Ty-2 that originated from L. hirsutum; six lines (Ty-52 and the FLA-prefixed) contained resistance genes introgressed from L. chilense; the origin of geminivirus resistance in entry 99S-C-39 is unknown. The FLA lines and 99-C-39 are not commercial quality but were included in case Ty-2 resistance did not hold up in these locations. Entries were planted in farmers’ fields under geminivirus pressure and evaluated for resistance and horticultural characters.

There are over 25 different tomato-infecting geminiviruses, including monopartite and bipartite forms. In India there are at least five distinct geminiviruses and numerous isolates within species. Project data has shown that the Bangladesh geminivirus is most closely related to the Bangalore and Gujarat geminiviruses but is a distinct virus in its own right. Host plant resistance can be the most effective and affordable means of geminivirus control, although virus diversity complicates resistance breeding.

In both the TNAU and CSA trials the twelve test lines were resistant to local geminiviruses but the fruit qualities of most were not suitable for local markets. Consumers prefer oblong-shaped fruits with large locules and a slightly acidic taste. H24 was acceptable in Tamil Nadu and large-scale seed production of this line is planned. CSA has requested additional lines of their preferred market type for evaluation.

In Bangladesh eight tomato lines, four exotic and four BARI released varieties were evaluated against ToLCV and vector, B. tabaci, in winter and summer season crops. The lines were TLB130, TLB111, TLB182, TLB133, BARI Tomato 1, 2, 5 and 10. Three exotic lines, TLB130, TLB133 and TLB182, showed a higher degree of resistance against ToLCV in the winter crop than the other varieties/lines tested. In the summer crop there was virus infestation in all lines tested but disease symptoms were less severe in the exotic lines than BARI varieties and the highest yields were recorded from the three exotic lines in both seasons, 49 to 62 tonnes/ha and 11 to 17 tonnes/ha for winter and summer crops of TLB130, 133 and 182. However, to get fruit setting from summer plantings it was necessary to apply hormone to all lines tested. BARI and TNAU is now in the process of developing varieties for general release based on the lines tested through the project.

Molecular diversity of tomato leaf curl viruses

Molecular diversity of tomato leaf curl viruses (ToLCVs) were fully analysed from the two main tomato growing areas of Jessore and Joydebpur in Bangladesh. The putative viral DNA was amplified from tomato plants exhibiting mild and severe symptoms by polymerase chain reaction (PCR) and the complete genomes of ToLCVs identified were sequenced. An isolate of the bipartite Tomato leaf curl New Delhi virus (ToLCNDV) was associated with the severe symptom phenotype from Jessore (ToLCNDV-[Jes]) while a previously undescribed monopartite virus, designated, Tomato leaf curl Joydebpur virus (ToLCJV), was sequenced from plants showing mild symptoms. ToLCNDV-[Jes] was closest to ToLCNDV-[Lucknow] at 95.7% and Tomato leaf curl Gujarat virus-[Varanasi] at 90.6% nucleotide (nt) identities based on DNA-A and -B component sequences. ToLCJV was similar to Pepper leaf curl Bangladesh virus at 87.1% DNA-A nt identity. Identification of ToLCNDV-[Jes] and ToLCJV was in addition to the previously described Tomato leaf curl Bangladesh virus with which they shared 73.2% and 86.0% DNA-A nt identities thus confirming the existence of at least three distinct viruses infecting tomato in Bangladesh. Nucleotide identities and placement in phylogenetic trees suggested that the viruses may have had different evolutionary pathways. The whitefly vector B. tabaci transmitted the viruses of this study equally efficiently. Four tomato varieties (TLB111, TLB130, TLB133 and TLB182) resistant/tolerant to South Indian ToLCV were screened against Bangladesh viruses. Although challenged by diverse viruses and potentially mixed infections, disease incidence remained low (6-45%) in resistant varieties compared to local cultivars (68-100%).

Root knot nematode, Meloidogyne incognita, IPM

Plant parasitic nematodes can cause particularly severe yield losses, typically up to 50 percent, as a result of root deformation which diminishes function and predisposes plants to other pathogens. In South Asia the root knot nematode, Meloidogyne incognita, is particularly devastatingwith a wide host range, generation times of typically between 20 and 30 days and females capable of producing a thousand eggs. Synthetic nematicides are notoriously toxic and expensive. In South Asia the nematostatic properties of African marigold, Tagetes erecta, are well recognized and some farmers grow the plant as an intercrop. However, the need to set aside productive land to grow T. erecta inevitably reduces yield.

Because T. erecta is grown on a commercial scale for flowers the possibility exists to use this plant material to control M. incognita in tomato. Cold aqueous T. erecta extracts were prepared by mashing plant material (ca 1 kg) with water (5,000 ml) and standing overnight. The aqueous extracts were filtered through muslin cloth and temporally stored in plastic containers (2,000 ml) before use. Aliquots (100ml) were applied to the base of susceptible tomato plants grown in M. incognita infested soil at 10 and 25 days after transplanting. The trials demonstrated that tomato plant height and leaf number were significantly improved in plants treated with T. erecta plant extracts and that whole plant extracts were more efficacious than stem extracts and that both were more effective than root extracts.


Infested Check

Treated with marigold extract	Treated with carbofuran

Root gall indices of tomato treated with T. erecta plant extracts were significantly less than untreated checks and comparable with a standard insecticide commonly used by farmers, carbofuran. Similarly, fruit yield from plants treated with T. erecta extracts were significantly more than untreated checks and comparable with carbofuran-treated plants.

SUSVEG-Asia