Screening for Resistance to Potato Virus Y and Potato Virus X in Potato (Solanum Tuberosum L.)

Abstract

Studies were conducted at KARI-Tigoni and KARI-Marindas (Molo) with the aim of assessing the value of using varieties with Potato Virus Y (PVX) and Potato Virus X (PVX) resistance in preventing crop losses under the local (Kenyan) potato growing conditions and also to assess suitability of these PVY and PYX resistant clones as resistant parents for developing new potato varieties in Kenya. In the first study, seven PVY and PYX resistant clones from the International Potato Centre (CIP) Lima, Peru together with six local susceptible check varieties were subjected to natural virus infection over three cropping seasons during Short Rains (SR) 2005 at KARI-Tigoni and in both sites (KARI- Tigoni and Molo) during the Long Rains(LR) 2006 and SR 2006. ELISA tests conducted on the tuber samples at the end of every season indicated significant (P = 0.05) higher percentage of 40 - 100% PVY and PYX infection in the susceptible check varieties and significant (P = 0.05) lower percentage of 0 - 5% infection in the best resistant clones. The CIP clones experienced significant (P= 0.05) lower yield reduction ranging from 1.2 to 2.3 T/ha compared to the susceptible check varieties which had a higher yield reduction of 12.2 to 15.4 T/ha. Among the CIP clones evaluated, CIP 394905.8 was found to be the best in with standing virus related yield losses since instead of experiencing a yield reduction like other genotypes; it experienced yield increase ranging from 0.83 to 1.2 T/ha in both sites of the study. In the second experiment, five CIP resistant clones were crossed with two susceptible cultivars and the progeny seedlings obtained were subjected to PVY and PYX sap inoculation to screen for virus resistance in the seedlings. Successful development of berries from the crosses was higher (ranging from 18.6 % to 61.5 %) in the crosses conducted in the field under lower temperature ranges of 12 - 31°C, 14 - 20 °C and 1118°C compared to the crosses conducted in the glasshouses (0 - 3.7 %) under relatively higher temperature ranges of 21 - 36°C and 18 - 31 °C. Number of true potato seeds obtained from the crosses and planted in each of the crossing combinations ranged from 1253 to 1791 and percentage emergence of seedlings ranged from 65 % to 90 %. Among the CIP clones used as resistant parents, CIP clone 395438.1 was identified as the best with 2 single dominant genes for PVY and PYX resistance out of four (Ry Ry ry ry) and it produced 84 % of resistant progenies when crossed with susceptible cultivar Tigoni. The studies recommended the utilization of PYY and PYX resistant clones/varieties in reducing virus related crop losses and as parents for developing new virus resistant genotypes.