Genetic and site effects on stem breakage in Pinus tecunumanii

Abstract

Fifteen provenance/progeny tests of Pinus tecunumanii (Schw.) Eguiluz et Perry were assessed for upper-crown stem breakage at 5 to 8 years of age in Brazil, Colombia and South Africa. Five year results indicated that the mean percent stem breakage was moderate in Colombia (14% to 21%), low in South Africa (2% to 6%) and very low in Brazil (<1%). In the Colombian tests, trees from provenances of Mexican origin were more susceptible to wind damage than those from Central America, 20% versus 14%. Provenance order of percent stem breakage at 5 years of age in Colombia was Montebello (27%), La Soledad (25%), San Jose (20%), Chempil (20%), Jitotol (18%), Las Piedrecitas (18%), Celaque (17%), Km 47 (16%), San Vicente (13%), San Jeronimo (13%), San Lorenzo (12%) and Las Trancas (7%). Two half-sib progeny tests assessed at 8 years of age in Colombia with trees from the Mountain Pine Ridge source of P. tecunumanii exhibited 13% stem breakage. Family variation in stem breakage ranged from 0 to 44% in Colombia and 0 to 33% in South Africa at 5 years of age and were highly significant. The Spearman rank correlations in stem breakage of 36 half-sib families common to tests in Colombia and South Africa were r=0.13 and not significant. Family heritabilities for stem breakage at 5 and 8 years of age ranged from 0.17 to 0.63. Results indicate that stem breakage was more common on trees with branches of large diameter and was not strongly related to growth rate.