Isozyme polymorphism: its role in genetic diversity studies and genome identification in selected important crops

Professorial Chair Lecture

Metro Manila Commission Professorial Chair Lecture

Date

2006

Abstract

To genetically characterize and determine the degree of diversity available in the different accessions of pili (Canarium ovatum Engl.), cashew (Anacardium occidentale Linn.), different Garcinia species, and new accessions of table- and cooking-type bananas (Musa spp.) from the National Plant Genetic Resources of the Institute of Plant Breeding, isozyme analysis was done using starch gel electrophoresis. The possible genome of the table-type banana cultivars was also determined.

Based on esterase (EST), acid phosphatase (ACPH), and alkaline phosphatase (ALPH), genetic variability was noted in pili from Albay, Camarines Norte, and Camarines Sur and in the 11 accessions of unknown origin. Six presumptive loci were determined. Percent polymorphism was 100%. Using a similarity coefficient of 0.60, the thirty accessions were divided into five clusters. Accessions of different origin grouped together which would indicate that variability exists in the accessions considered.

To further prove that genetic diversity exists in pili, twenty-five accessions collected from Oas, Albay were also subjected to isozyme analysis. Eighteen presumptive loci were determined; three for glucos-6-phosphatase dehydrogenase (G6PD), two for EST, phosphogluconate dehydrogenase (PGD), malate dehydrogenase (MDH) ACPH, ALPH, and phosphoglucomutase (PGM), and one for glutamate oxaloacetate (GOT), phosphoglucoisomerase (PGI), and alcohol dehydrogenase (ADH). Considering a similarity coefficient of 0.70; four clusters were obtained although the 25 accessions were collected only from Oas, Albay. This would indicate that accessions were genetically different. Pili being dioecious is an obligate cross-pollinating crop. Percent polymorphism was 83.33% and fifteen of the presumptive loci were polymorphic. Only ALPH2, G6PD2, G6PD3 were monomorphic. The observed heterozygosity for ACPH1, ACPH2, ALPH1, EST1, EST2, and PGD2 was higher compared to the expected heterozygosity.

Using seven enzymes, fourteen presumptive loci were identified in sixteen accessions of cashew from Palawan, Zambales, Los Banos. Two zones of activity were observed for ACPH, ALPH, EST, IDH, SKDH, PGD, and PGM. ALPH1, ALPH2, IDH1, IDH2, PGD1, PGD2, PGM1, and PGM2 were all monomorphic. Using a similarity coefficient of 0.91, the 16 accessions were grouped into two clusters. Nine accessions from Zambales were included in the first cluster together with two accessions from Palawan and Los Banos. The second cluster is composed of two accessions from Zambales. The coming together of the different accessions in cluster would indicate that they are genetically the same.

The genetic relationship of five Garcinia species namely G. mangostana, G. binucao, G. kydia, G. lateriflora, and G. tinctoria was established using 13 enzyme systems. Based on 28 presumptive loci composed of ACPH1, ACPH2, ADH1, ADH2, ALPH1, ALPH2, EST1, EST2, G6PD1, G6PD2, GDH1, GDH2, GOT1, GOT2, GOT3, IDH1, IDH2, MDH1, MDH2, MAL1, MAL2, MAL3,PGI1, PGI2, PGM1, PGM2, SKDH1, and SKDH2, two clusters were obtained using a similarity coefficient of 0.73. Cluster 1 is composed of G. mangostana and G. tinctoria. Cluster 2 is further grouped into two, the first group is composed of G. binucao while the second group is composed of G. kydia and G. lateriflora. G. mangostana was found to be related to G. tinctoria while G. kydia was more related to G. lateriflora.

Isozyme profiles of twenty-one table-type and six cooking-type banana (Musa sp.) cultivars were studied. The different isozymes used include malate dehydrogenase (MDH), 6-phosphogluco dehydrogenase (PGD), phosphoglucoisomerase (PGI), and phosphoglucomutase (PGM). Different banding patterns were observed. Banding patterns (BP) of the different cultivars with known genomes (19) were compared with newly collected cultivars (5 table-types; 3 cooking-type) with unknown genome to determine the genome identity of the latter. The genomes of the five table-type cultivars were identified. The genome Latundan Puti (LPT), Manang Costa (MCS), and Kinamalay (KMY) is AAB based on MDH and PGI. Both the genome of Manifun (MNF) and Mangipod (MPD) is AAA based on MDH, PGI, and PGM. The four isozymes were not useful in identifying the genome of the three cooking-type cultivars namely, Balatay (BLT), Bataaan (BAT), and Dumanese (DUM). Using NTSYS with similarity coefficient of 0.85, a dendrogram was constructed. The correct genome of the five table-type cultivars was further verified based on the cluster obtained. The cultivars with unknown genome (MCS, LPT, and KMY) form a cluster with cultivars with AAA and AAB genomes. MCS, LPT, and KMY were identified to have AAB genome. MPD identified to have AAA form a cluster with LAT (AAB). Only MNF identified to have AAA clustered with BUN (AAA). The clustering of cultivars with AAA and AAB genome may indicate common genomic origin.

Location

UPLB Main Library Special Collections Section (USCS)

College

College of Arts and Sciences (CAS)

Language

English

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