An EST-SSR marker, bu099658, and its potential use in breeding for yellow rust resistance in wheat

EST-SSR markers, derived from the A and B genomes of wheat were used to identify molecular markers associated with yellow rust resistance. For this purpose, bulk segregant analysis was performed using 114 EST-SSR primer pairs. They were screened on the parent genotypes and resistant/susceptible DNA pools from the cross between Izgi2001 (resistant male parent) × ES14 (susceptible female parent) at the seedling and adult plant stage. An EST-SSR marker, bu099658, generated the 206 bp DNA fragment that was present in the resistant parent and resistant bulk, but it was not present in the susceptible parent and the susceptible bulk. To investigate its association with Yr genes, 20 individuals of NILs were also amplified with BU099658 and the 206 bp marker fragment was obtained only in Yr1/6 × Avocet S. Additionally, bu099658 was screened on 65 genotypes which possessed different Yr genes/gene combination(s) and Yr1. The results indicate a close linkage of bu099658 with the Yr1 gene.

Identification of rapd marker linked to blast resistance gene in a somaclone of rice cultivar Araguaia

The gene Pi-ar confers resistance to Pyricularia grisea race IB-45 in a somaclone derived from immature panicles of the susceptible rice (Oryza sativa) cultivar Araguaia. RAPD technique was used to identify molecular markers linked to this gene utilizing bulked segregant analysis. Initially, the two parental DNAs from the resistant donor SC09 and 'Araguaia' were analyzed using random primers. Of the 240 primers tested, 203 produced amplification products. The two parental DNAs along with the resistant and susceptible bulks of F2 population were screened using 48 primers that differentiated resistant and susceptible parents. Even though eight primers differentiated the resistant bulk from the susceptible bulk, as well as somaclone SC09 and 'Araguaia', only one primer, OPC02 ('GTGAGGCGTC'), was found to be tightly linked (1.7cM) to the resistance gene of somaclone SC09.

Identification of Genetic Markers in Olive Linked to Olive Leaf Spot Resistance and Susceptibility

Olive leaf spot is a disease of olive (Olea europaea L.) caused by the fungal pathogen, Spilocea oleaginea Cast. Progeny derived from crosses among susceptible, resistant, and semiresistant parental lines were assessed in the field for 8 years and classified as either resistant or susceptible. DNA from some of the progeny of this segregating population was used to identify molecular markers linked to olive leaf spot disease using the randomly amplified polymorphic DNA (RAPD) technique and bulked segregant analysis (BSA). Two DNA bulks were constructed, each containing 13 progeny showing either resistance or susceptibility for the disease, and screened for polymorphisms using 100 primers. One primer produced two polymorphic bands, one of ≈700 base pairs (bp) from the susceptible bulk and the other of ≈780 bp from the resistant bulk. The 780 bp marker appeared in 70.6% of the segregating progeny and 100% of parents showing resistance to leaf spot disease, while the 700 bp marker appeared in 47.1% of the segregating progeny and 100% of the parents showing susceptibility. These markers can be used as screening tools in olive improvement programs.

079 Molecular Tagging of ZYMV Resistance in Squash (Cucurbita moschata)

Marker-based selection for resistance to zucchini yellow mosaic virus in squash (Cucurbita spp.) would allow breeders to screen individual plants for resistance to multiple viruses. The C. moschata landrace Nigerian Local is widely used as a source of resistance in C. pepo breeding programs. We used RAPDs and bulk-segregant analysis to screen two BC1 populations for a marker linked to the dominant major gene for resistance from Nigerian Local. The initial cross was Waltham Butternut × Nigerian Local; the test populations were created from reciprocal backcrosses to Waltham Butternut. Both populations segregated 1:1 for resistance when hand-inoculated with ZYMV. RAPD primers were screened on a resistant bulk and a susceptible bulk from each population, and Waltham Butternut and Nigerian Local. Primers that gave bands linked to resistance were further screened using DNA from individual plants in each population. The potential markers will be tested on several populations derived from crosses between summer squash (C. pepo) and Nigerian Local to determine if they would be useful for selection in a C. pepo background.

IDENTIFICATION OF A RAPD MARKER LINKED TO THE ROOT KNOT NEMATODE-RESISTANT GENE IN SWEETPOTATO

The inheritance of root-knot nematode race 3 [Meloidogyne incognita (Kofoid & White) Chitwood] resistance was studied in 71 progenies of the F1 backcross population produced from the resistant parent `Regal' and the susceptible parent `Vardaman'. The distribution frequency of the progenies measured on total nematode number (eggs + juveniles) indicated a bimodal distribution with a ratio of 4 resistant: 1 susceptible. Based on this phenotypic ratio, the proposed genetic model was duplex polysomic inheritance (RRrrrr = resistant). Bulk segregant analysis in conjunction with the RAPD technique was employed to identify RAPD marker linked to the root knot nematode-resistant gene. Nine of 760 random decamer primers screened showed polymorphic bands. Primer OPI51500 produced a band in the resistant bulk, but not in the susceptible bulk. Estimated recombination frequency of 0.24 between the OPI51500 marker and the root-knot nematode-resistant gene indicated linkage.