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Titre : Características bioquímico-fisilógicas de la germinación y desarrollo de plantas jóvenes de maguey (Agave) y su relación con la especie, temperatura y potencial de agua del sustrato.

BIOCHEMICAL AND PHYSIOLOGICAL CHARACTERISTICS OF GERMINATION AND DEVELOPMENT OF YOUNG PLANTS OF MAGUEY (Agave) IN RELATION TO SPECIES, TEMPERATURE AND SUBSTRATE WATER POTENTIAL.

Auteur : Ramírez Tobías, Hugo Magdaleno

Université de soutenance : Colegio de Postgraduados (COLPOS)

Grade : Doctoral Thesis 2011

Résumé
Physiological processes such as germination and growth of Agave species are modified by environmental factors according to the climatic conditions at the sites of species distribution. To test this hypothesis, seed germination of eight Agave species in a temperature and water potential (ψ) gradient, from 10 to 40 °C and from -0.03 to -1.5 MPa, respectively, under laboratory conditions, and the effect of high and low substrate ψ (-0.7 and -3.5 MPa, in average) in young plants of the same species for 14 months, in greenhouse conditions, were evaluated. Maximum cumulative germination (AG) (90% or higher) was recorded around 25 °C and at -0.03 MPa after 80-190 h, except A. angustifolia ssp. tequilana which reached 26% at 30 °C. Maximum AG in A. Americana, A. lechuguilla, A. striata and A. salmiana remained similar (p>0.05) between 15 and 33 °C at -0.03 MPa and between -0.03 and -1.5 MPa at 25 ºC ; whereas in A. asperrima and A. cupreata maximum AG occurred only between 15 and 25 and 25 and 30 °C, respectively, at -0.03 MPa, and at -1.5 MPa at 25 °C it dropped to 30%. Young plants in the restrictive substrate (ψ averaging -3.5 MPa, but dropped from -0.7 to 6.0) : (1) duplicated (p<0.05) radical proline content, up to 1 mol100 mg-1, except A. lechuguilla and A. striata, (2) four species increased (p<0.05 ; until 0.46) the root:shoot index, while in three it index remained similar and in another it was reduced (p <0.05 to 0.17), (3) eighth leaf thickness was maintained in comparison with plants kept under hydrated condition (-0.7 MPa). The total dry biomass per plant was reduced (p<0.05, from 68 to 28 g) in all of species under water restriction, however, the number of leaves per plant of A. angustifolia ssp. tequilana and A. salmiana (14 and 10), and plant coverage of these species and of A. lechuguilla and A. duranguensis (0.222, 0.043, 0.017 and 0.185 m2 pl-1) remained unchanged. Tolerance of Agave spp. germination to slightly severe temperatures and water restriction was evident ; it is broad, restricted and/or skewed depending on the climate of species distribution. The increase of biomass root proportion and proline root content, in part, and maintenance of leaf thickness (a turgor indicator) are Agave responses to tolerate the moisture restriction. Low water availability inhibits the total biomass accumulation ; despite of this, species adapted to aridity or to wider environmental conditions can maintain the growth (number of leaves and plant cover) under this condition.

Mots clés : Agave Germinación óptima Crecimiento Restricción de humedad Tolerancia ambiental Reacción fisiológica y morfológica Optimum germination Growth Moisture restriction Environmental tolerance Physiological and morphological responses

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