Deep seeding resistance in maize: selected after domestication or a strategy of its wild ancestors to escape underground animal burrowing?

Résumé fourni par la source

Buried seeds avoid predation ensuring their survival until conditions are suitable for germination. The ability of seedlings to emerge from the soil depends on soil characteristics, burial depth, and the skotomorphogenic program of each species. This process is of interest to agriculture, as deep planting is practiced in wheat, sorghum, oats, and maize crops in certain arid and semi-arid regions of the world. In maize, deep planting can range from 10 to 40 cm, and only certain landraces are competent for this practice. It is known that deep-planting resistant varieties exhibit exaggerated mesocotyl elongation, but it is unclear whether resistance to deep planting has selected positively or negatively the growth capacity and/or development of other seedling organs and whether deep-planting resistance is an ancestral trait in Zea or evolved after maize domestication. To determine the skotomorphogenic patterns in the subtribe Tripsacinae, deep planting trials were conducted with representatives belonging to the genera Zea and Tripsacum and the length or number of seedling organs measured. The majority of maize seedlings grown in darkness exhibited features that we refer to as quasi-photomorphogenic (i.e., rupture of the coleoptile tip by the first plumular leaf and development of adventitious roots at the coleoptilar node [ARCN]), unlike teosintes that displayed a small proportion of individuals with the quasi-photomorphogenic phenotype or species of Tripsacum that maintained a strict skotomorphogenic phenotype prior to emergence. Moreover, ARCN were absent in Tripsacum and rare in teosintes, while seminal roots were uncommon in both Tripsacum and teosintes. In Tripsacinae, relative deep sowing depth (RDSD) for seedling emergence correlated positively with mesocotyl and stem lengths. Moreover, RDSD correlated negatively with the number of ARCN and SR and the length of the primary root and, to a lesser extent, of the coleoptile. In maize, SR development primordia ensued both embryonically and post-embryonically. These findings indicate that emergence from deeper soil depths has influenced the growth and development of all seedling organs, not just the mesocotyl, and that deep planting resistance is a characteristic that appeared within the Zea genus prior to maize domestication. Further, we report that Tripsacum caryopses are dispersed by myrmecochory and teosinte caryopses by seed-caching rodents. The ecological significance of skotomorphogenic development programs that aid in the escaping of wild Tripsacinae seedlings, from underground caches made by their animal dispersers, is discussed.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.