Cuartero Zueco, J.

Gil Ortega, Ramiro

Palazón Español, Carlos Fernando

citaREA Repositorio Electrónico Agroalimentario

- 141 -RESPONSE OF PEPPER TO THE INTRAVARIETAL SELECTION FOR RESISTANCE TO PHYTOPIITHORA CAPSICI (1) R. Gil Ortega, C. Palazón Español S.I.A . - D.G.A., Apartado 727 50080 Zaragoza, Spain. Abstract J. Cuartero Zueco Estación Exp. 'La Mayora' (C.S.I.C.) Algarrobo- Costa (Málaga), Spain. When pepper line PI201232, resistant to Phytophthora capsici, was inoculated with zoospores of Bl, a sufficiently aggressive isolate of that parasite, it was possible to cause some mortality of plantlets almost invariably. Progenies of the surviving plantlets displayed higher levels of resistance in comparison to the source material, line PI201232. ün the other hand, line Serrano Criollo de Morelos- 334 was not attacked by isolate Bl, while it was partially infected by isolate 8303 of Mexican origin. It seems that resistant lines display variabili_ ty when inoculated with a sufficiently aggressive isolate. That variability was also displayed when susceptible pepper lines were inoculated with isolate Ca, -less aggressive than Bl. The implications of these results in the analysis on thé genetics of the character are discussed. Research efforts have long been made in pepper breeding for resistance to Phy-tophthora capsici. It was in 1960 when Kirnble and Grogan reported PI123469, PI201232 and PI201234 as resistant materials. Later on,Smith et al. (1967) and Pochard and Chambonnet (1972) suggested that resistance was governed by one or two major genes, although the presence of other modifying genes was necessary to explain some aspects of that mechanism. In Mexico, Guerrero and Laborde (1980), using autoctonous isolates of P. capsici, did not find any resistance on the material considered by the above mentioned authors. However, Guerrero and Laborde (1980) reported a new source of resistance controlled by two independent, recessive genes in the variety Serrano Criollo de Morelos. Consequently, there is a certain contradiction concerning the genetics of the character. ün the other hand, resistant materials are not always 100 per 100 resistant (Kirnble and Grogan, 1960; Guerrero and Laborde, 1980). If these materials could be selected to obtain more homogeneously resistant lines, they would be more adequate to explain the genetics of the character anda better material to introduce resistance into commercial varieties. With these objectives, sorne experiments have been developed. In all of them,inoculations were made with a zoospore suspension as described by Kirnble and Grogan (1960), but ata much hi~ er concentration that that used by these authors. We used 60 x 40 x 8 cm trays containing 200 to 300 plantlets belonging to eigtit different lines. Inoculation was made by pouring 500 ml of a zoospore suspension ata concentration of 300,000 zoospore/ml. (1) Experiments presented here have been partially sporisored by CAICYT and INIA. - 142 -TABLE 1. Percentages of mortality in several pepper lines inoculated with dife-rent isolates of P. capsici . Isolate Line Bl(l) Ca(l) SUSCEPTIBLE LINES 100 30- 95 BREEDING LINE - NQ 2 40-80 0-25 - Phyo 636 0-80 o - Línea nº 10 0-60 0-5 RESISTANT LINE - Línea 29 0- 10 -- PI201232 0-30 0-5 - PI201234 0- 25 o - Serrano Criollo de Morelos-334 0- 5 o (1) Intervals are given as a sumrnary of several experiments. (2) Data from only one experiment. 8303 ( 2) 100 100 100 100 100 100 100 33 In the first experiments, P. capsici strain Bl, isolated from pepper in Spain, was u.sed. This isolate is one of the most aggressive ones in our collection. It was inoculated on different pepper lines, including susceptible (Morrón lines INIA 65- 4, INIA 106, INIA 224 and INIA 225) resistant (Linea 29, PI201232, PI201234 and Serrano Criollo de Morelos-334) and breeding lines (NQ 2, Phyo 636 and Linea NQ 10). 0ne month after inoculation, the mortality percentages showed that even the most resistant lines could produce sorne susceptible plants (Table~ . Plantlets surviving from these experiments were selfed. Their progenies and source lines were inoculated again with isolate Bl. Tfie mortality average in progenies was lower than in their respective source lines (Table 2). Most proge-nies showed no mortality (61 cases out of 89). Only three of the 28 remaining ones hada higher mortality than their source lines. These three cases may be explained by escapes to infection in the source line. Therefore, we can con-elude that, in general terms, all the varieties studied responded to selection for higher resistance to isolate Bl in only one generation. Variability was not - 143 -TABLE 2. Percentages of mortality in different source lines and progenies of se-lected plants, all inoculated with the isolate Bl. S O U R C E L I N E PERCENTAGE SUCEPTIBLE LINES 100 BREEDING LINE - NQ 2 51 - Phyo 636 23 RESISTANT LINE - Línea 29 2 - PI201232 13" - PI201234 8 - Serrano Criollo de Morelos 334 o PROGENIES OF PLANTS WHICH SURVIVED AFTER INOCULATION OF THE ABOVE MENTIONED --SOURCE LINES NUMBER LEVELS OF RESPONSE SOuRCE LINE OF (PERCENTAGE OF PROGENIES MORTALITY) NQ 2 8 o 5 1- 10 10 11- 30 3 31- 60 2 61 - 100 Total =28 x = 26 Phyo 636 10 o Línea 29 14 o PI201232 8 o -- 5 1- 10 1 1 11 -30 Total • =14 x = 4 PI201234 10 o 2 1- 10 Total =12 x = 1 Serrano Criollo de Morelos 334 11 o - 1 44 -evidenced either in susceptible lines which showed 100 per 100 mortality when inoculated with isolate Bl, or in Serrano Criollo de Morelos- 334 which showed virtually no mortality. However, in susceptible or highly resistant lines, there are signs of the genetical variability already found in the other materials. For instance, when inoculating the same collection of varieties with isolate Ca, one of our less aggressive isolates of P. capsici obtained fran pepper, sorne of the suscep-tible material survived (Table 1). Moreover, when using sorne Mexican isolates of -P. capsici susch as 8303 (supplied by Guerrero Moreno, INIA Mexico, through INRA), -susceptible material, breeding lines and most resistant lines became cornpletely susceptible, while Serrano Criollo de Morelos- 334, which was not at all or slightly attacked by isolates Bl and Ca, became partially 'Susceptible (Table 1). We estimate that 100 per 100 resistant lines to isolate Ca could be selected from the above mentioned susceptible lines as it has been shown for isolate Bl on sev-eral lines and PI materials. The same can be applied to Serrano Criollo de More-los- 334 with isolate 8303. Actually, we have selected Serrano Criollo de More-los- 334 plants surviving to isolate 8303andtheir progenies will be inoculated with this isolate in order to prove that hypothesis. These results show that there exists sorne variability in terms of resistance to P. capsici in sorne resistant lines such as PI201232 and PI201234 usually employed in breeding programs. This variability was eliminated and lines completely re-sistant to isolate Bl were selected when source lines resulted infected by that isolate in such a way that it caused neither absolute mortality nor total surviv-al. The quick response to selection for resistance suggests that the number of genes involved is small. However, this is only a hypothesis which must be check-ed. References GUERRERO-MORENO A., LABORDE J.A., 1980. resistance to P. capsici in Mexico. Wageningen, 52- 56. Current status of pepper breeding for Fourth Eucarpia Capsicum Meeting, KIMBLE K.A., GROGAN R.G., 1960. Resistance to Phytophthora root rot in pepper. Plant Disease Reporter, 44 (11), 872- 873. POCHARD E., CHAMBONNET D., 1972. Méthodes de sélection du piment pour la résis-tance au Phytophthora capsici et au virus du Concombre. First Eucarpia Meeting on Genetics and 8reeding on Capsicum. Universitá du Torino, 270- 281. SMITH P.G., KIMBLE K.A., GROGAN R.G., MILLET A.H., 1967. Inheritance of resist-ance in peppers to Phytophthora root rot. Phytopathology, 57, 377- 379-

Response of pepper to the intravarietal selection for resistance to Phytophthora capsici

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Response of pepper to the intravarietal selection for resistance to Phytophthora capsici

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