GENETIC DIVERSITY, MICRO PROPAGATION, AND COLD HARDINESS OF ILEX GLABRA (L.) A. GRAY

GENETIC DIVERSITY, MICRO PROPAGATION, AND COLD HARDINESS OF ILEX GLABRA (L.) A. GRAY

By Youping Sun

Thesis Advisor: Dr. Donglin Zhang

An Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Doctor of Philosophy

(in Plant Science)

May 2010

Ilex glabra(L.) A.Gray (inkberry) is a native evergreen shrub with dark green foliage and compact habit. This shrub has gained popularity in the northern landscapes of the United States. To better understand genetic relationships among inkberry cultivars and breed cold-hardy cultivars for northern landscape, the following projects were conducted.

Forty-eight inkberry accessions and two other Ilex species (Ilex crenata Thunb. and I. mutchagara Makino) were studied using amplified fragment length polymorphism (AFLP) markers. Based on both morphological and molecular data, all inkberry accessions were classified into six groups including, a wild species group and five cultivated groups, ‘Densa’, f. leucocarpa, ‘Pretty Girl’, ‘Shamrock’ and ‘Viridis’.

Inkberry was hybridized with Ilex verticillata (L.) A. Gray (common winterberry) and Ilex × meserveae S.Y. Hu (meserve holly) to increase their cold hardiness. Inkberry ‘Chamzin’ and ‘Densa’ had higher compatibility with eithercommon winterberry or meserve holly, while inkberry wild species and its cultivar ‘Compacta’ were less compatible, and ‘Nigra’ and ‘Shamrock’ were almost incompatible. Reproduction barriers, including the inhibition of pollen germination, pollen tube growth to the style and the ovary, and lack of fertilization, resulted in the cross incompatibility.

The micropropagation procedurewas successfully producedfor commercial production of new inkberry cultivars.Nodal segments containing one axillary bud (1-1.5 cm) of inkberry were established on a Murashige and Skoog (MS) medium without hormones. The sprouted shoots (~1.0 cm) were proliferated on MS with 4.5 μM ZT followed by in vitro rooting on ¼ MS plus 10.3 μM IBA. Rooted plantlets were then transplanted into a mix of peat moss and perlite (1:1 v/v), acclimatized in a mist system for four weeks, andgrown in a pot with Metro-mix under greenhouse conditions for 10 weeks.

Cold hardiness of inkberry cultivars were conducted in both field trials and laboratory tests. ‘Shamrock’ was the most cold-hardy cultivar; f. leucocarpa, ‘Viridis’, and ‘Nigra’ were the least cold-hardy cultivars; while ‘Compacta’, ‘Densa’, ‘Chamzin’, ‘Pretty Girl’, and wild species had intermediate cold hardiness. Laboratory test could be used to reliably predict the cold tolerance of inkberry cultivars in the field.