Identification of Peach Genotypes (Prunus persica (L.) Batsch) in the North-Central Region, Mexico

RESULTS AND DISCUSSION

Morpho-physiological traits and productivity analysis: Table 1 shows a brief description of the used genotypes according to investigated traits such as place of origin, ripening, οBrix, fruit firmness, weight and color. Identified genotypes as early maturing were harvested between 15th of June and 15th of July; intermediate genotypes were harvested between the 16th of July and 15th of August; and late maturing genotypes were harvested after the 16th August. Comparing among the genotypes of the early maturing group, Roxana was found superior on fruit quality and higher yields (41.6 kg tree^-1). Likewise, San Gabriel (C-161) was the best among the genotypes from intermediate maturing group with yields of 54.67 kg tree^-1 and good fruit weight (121.5 g). In the late maturing group, Zacatecas landrace (C-234) showed the highest fruit weight (162.3 g); although, yields were poor (13.64 kg tree^-1).

Two groups arose from the morphological trait analysis were obtained (data no showed). San Gabriel (C-3) was placed in Group I; nevertheless, this genotype seemed to be independent since it showed protuberance, high abscission rate, erectile plant growth, small fruits (60.7 g fruit^-1) and shorter maturation period as compared to other genotypes within the early maturation group. Group II was characterized by horizontal branching, higher fruits and different maturation behavior. This morphological analysis allowed finding the relationship between genotypes obtained from different sites from Aguascalientes and Zacatecas. As an example, San Gabriel (C-167) and Zacatecas landrace C-175 are different only on the maturation period the rest of the characteristics appeared the same; furthermore, San Gabriel coded as C-175 and C-176 were very similar in both maturation and fruit firmness.

Fig. 1:	RAPD analysis on peach genotypes (Prunus persica L. Batsch) grown by means of 14 primers OPM series: OPM-10 (A) and OPM 12 (B) in Central North Mexico region

Other findings were: both genotypes C-1 and C-229 (from Guanajuato and Zacatecas, respectively) showed the lowest fruit firmness. Genotypes C-164 and C-172 (San Gabriel) were slightly different on ^οBrix. Finally, Roxana (C-4) and San Gabriel (C-163) were similar on the maturation period.

RAPDs analysis results: Amplification of 14 fragments was obtained using primers OPM-12, OPM-10 and OPM-16, while using primers OPM-14 and OPM-18 yielded only 3 discrete bands each (Table 2). In general, amplicons ranged approximately from 300 to 4070 bp in size. Some of them were found to be genotype-specific as shown in Table 2 and Fig. 1a, b. Genotype-specific fragments shown were for genotype C-277 (3054 bp amplified with OPM-18) and genotypes C-175 and C-234 (5054, 2036 bp, respectively) amplified with OPM-13 (no showed). Fortunately, the above mentioned genotypes have good qualities for breeding (Table 1). Once the dendrogram was obtained using only the polymorphic fragments, it was evident the presence of two main groups: Group I includes only to genotype C-279 which is a Prunus domestica (May Bell Plum) imported from South Carolina USA, while Group II includes to the rest of the genotypes (Prunus persica) (Fig. 2a).

Fig. 2:	(a) Dendrogram obtained from 24 peach (Prunus persica) genotypes grown in the Central-North region of Mexico, (b) C-167 and (c) C-233

Genotype C-6 (NG) and C-227 (Zacatecas landrace) showed the similarity coefficients highest (0.97349). In spite of that similarity, these genotypes differ on fruit firmness and maturation period. Low similarity coefficients (0.6091 and 0.6122) were obtained when compared genotypes C-279 to genotypes C-6 (CP-9116C) and C-227 (Zacatecas landrace), respectively. Among peaches, the lowest similarity values (0.8584 and 0.8622) were found when genotype C-176 was compared to C-4 and C-161, respectively. These results would be indicative of the close genetic relatedness of the peach genotypes grown in the Central-Northern Region of Mexico.

DISCUSSION

Due to the high cross pollination rate present in the genus Prunus spp., new genotypes can be developed with higher yields or better fruit quality. This breeding process could be accelerated if assisted by molecular markers associated with desired traits (Jun et al., 2002), helping in the process of selecting candidates from germinating plants. At the same time, molecular marker analyses would help on standardization for genotype naming or labeling all over Mexican peach production regions, in order to avoid confusion and promoting conservation of valuable gene sources. This study is considered the one of the first attempts in Mexico for establishing genetic fingerprints on peach that may help on taking decisions for potential introduction of the appropriate cultivars for the specific regions. It may be a good start focusing on the genotypes with higher yields and good fruit quality such as Roxana (C-4) from the early maturing group, San Gabriel (C-172) from the intermediate maturing group and a Zacatecas landrace (C-234) from the late maturing group as model for peach breeding. Indeed, the remaining samples were differentiated and clustered together as a group of cultivars or genotypes without any significant relation to some botanical or agricultural traits as is indicated by Raddova et al. (2003) when analyzed peaches provide by different countries. Better distinguishing results were detected by means of other amplification strategy in the work of Jun et al. (2002) were they found RAPDS and SCAR markers linked to the flesh adhesion gene (F) in peach (Prunus persica) and Cheng (2007) classified the peach groups as yellow, honey, flat, red leaf, crisp, bitao and juicy. In the future, the local collection from peach (Prunus spp.) growers will be extended and probably will be used for further plant breeding (gene identification o genetic transformation) activities.

ACKNOWLEDGMENTS

Thanks to Eng. Leonel Quesada Parga and Aguascalientes peach growers for their support to C.M. Melgoza Villagómez while pursuing her Master´s degree at the ITEL. Our thanks to Eng. Pablo Arturo Alemán and Eng. Alberto Peralta Bringas for the help provided. Finally, we appreciate the great labor provided by Dr. Pérez y Dr. Rodríguez, since some genotypes were obtained by their peach breeding programs.