Researcher: Vaino Poysa, GPCRC

Objectives:

1) The identification and evaluation of desirable traits, including superior resistance to the prevalent diseases of tomato, especially bacterial canker and anthracnose, and processing quality attributes, in unadapted accessions, related species, and lines derived from interspecific crosses.

2) The transfer of these traits to Lycopersicon esculentum, and their incorporation in genetic backgrounds well adapted to Southwestern Ontario.

Methodology:

Two tests were conducted to evaluate resistance to bacterial canker and powdery mildew. For bacterial canker, 22 breeding lines were inoculated with a bacterial canker spore suspension injected into the stem, using a syringe, two weeks after field transplanting. Disease symptoms were rated twice, once at flowering time and once during the fruiting period. For powdery mildew, 43 breeding lines were inoculated at the 3-4 leaf stage with a powdery mildew spore suspension at the concentration of 4.5 x 10⁴ spores/mi and then kept in the growth chamber for 24 hours at near 100% RH by automatically turning on the humidifier every 2 hours. Disease symptoms were rated 10 days after inoculation based on a 0-5 scale. Anthracnose resistance was rated as described in 1999.

Results:

Three populations, including the L. hirsutum line, LA2 157, were rated as nearly completely resistant to bacterial canker (rating of 1.0), while an additional three lines had ratings averaging less than 2.0. For powdery mildew, three lines were rated as resistant as selections from the Dutch greenhouse tomato hybrid, DRW 4409, which possesses a single dominant gene for resistance to this pathogen. Development of molecular markers to assist in the breeding efforts and characterization of the various sources of resistance is continuing.

For anthracnose, among the F2 populations resistance was apparently recessive and controlled by several genes, as only about 10% of the plants were evaluated as resistant in more than half the populations. Only in the cross TD98-0l 14-1 were major resistance factors identified, as about 45% of the plants were rated 1. Among the F3 lines, lines derived from crosses TD970045 and TD970053 had over 80% of the plants rated as resistant. The resistance in the cross TD970045 was derived from 83B237 and 76B494-2, the two anthracnose resistant lines from USDA, Beltsville, while the resistance in TD970053 was also derived from 83B237. The best F5 line, TD940465, also has its resistance derived from Beltsville sources. The best advanced lines, DA94-0463-1-1-1-2-4, 85.404-14112511-0-2, and DA94-0455-1-2-4-1-1, had all plants (100%) showing a resistant reaction to anthracnose. The first two lines had their resistance derived from Beltsville sources while the last came from OTT.151. In this evaluation, the breeding lines showed much higher frequency of plants manifesting resistance compared to the control commercial cultivar. Moreover, it is shown from these populations that only a small percent of populations in F2 and F3 had >40% resistant plants rated as "1 ", whereas in F5 and the advanced lines majority of the populations had at least 60% resistant plants rated as "1", which reflects the efficiency of the selection pressure applied to these population.

Seeds of these lines will be distributed to UG-RCAT and private breeders.

Interspecific lines

In 2000 we grew 16 separate tests to evaluate interspecific breeding materials, at various stages of development, derived from L. pimpinellifolium, L. cheesmanii, L. chmielewskii, L. parviflorum, L. hirsutum, L. peruvianum, and Solanum pennellii for agronomic performance and fruit quality. From these approximately 650 populations, we selected some 420 plants for further evaluation.

Hybridization

In 2000 we made several crosses in the field, including interspecific x adapted, breeding selections x adapted and various back crosses. These crosses are very useful materials for transferring a range of traits (anthracnose resistance, bacterial canker tolerance, high solids, as well as several interspecific crosses to broaden the genetic base of adapted tomatoes) to tomato backgrounds well adapted to Southwestern Ontario. Several of the attempted crosses failed to set seed-bearing fruit and will be re-done in the greenhouse during the fall-winter period.

Development of molecular markers linked to disease resistance

In order to facilitate breeding for disease resistance in tomato, a project to identify molecular markers linked to resistance genes for tomato diseases such as powdery mildew, anthracnose and bacterial canker has been initiated. The screening of simple sequence repeat (SSR) or microsatellite primers is in progress; some of the SSR primers screened produced good polymorphisms among the parental materials, indicating that they will could be useful as markers.