INTRODUCTION

Medicago and Trifolium species are the most valuable crops of the rangelands. These species have the ability of yielding quality forage as well as fixing at least 120 kg N per ha resulting in increased soil fertility^[1].

Annual Medicago species are known collectively as “medics”. Medics are evolved in North Africa and Middle East where they grow over a wide range of soils, temperature regimes and lengths of growing season^[2]. Most medic species are winter annuals adapted to Mediterranean climates^[3]. Self seeding annual legumes may be better adapted than perennial legumes to arid rangelands. Kebe and Smith indicated that the medics are reasonable rangeland plants even in the arid regions where annual rainfall is about 110 mm^[4]. The medics and related species as reseeding legumes are spread over very wide range of areas in the world owing to a great adaptation capability^[5-7].

Medic pastures that produce high levels of good quality forage are well suited to grazing and are used extensively throughout dryland farming regions of the world. In these regions, they are normally an integral component of cropping rotations ^[7,8].

Annual clovers are accepted as very valuable forage plants in many countries, especially in Mediterranean regions. However, these plants, as in medics, have hard seed coats and low germination rate, when subjected to inadequate environmental conditions^[9,10].

The most important germination problem of the seeds of forage legume crops that are used in over seeding, artificial rangeland and lay farming is that these plants have very hard seed coats. Trifolium and Medicago species may have hard seededness at a rate of 100% according to eco-types^[7,11]. Many legumes produce indehiscent fruit (pods) that break down slowly and prevent moisture from being absorbed by rapidly the seeds^[12]. This trait, along with hard seededness mechanism, allows a proportion of a seed population to survive even in extended drought and promotes germination^[13]. Quinlivan showed that medics could survive for many years of drought due to the hard seed mechanism^[14].

There is a lack of research on breaking dormancy of hard seededness in forage legume crops. Muir and Pitman stated that the most effective methods of breaking dormancy of hard seed of legumes were sulfuric acid and mechanic scarification^[15]. Horowitz and Taylorson^[16], Mujica and Rumi^[17] indicated that one of the most effective methods in breaking hard seededness dormancy in the seeds of medic species was mechanical disruption of the seeds. Cabrales and Bernal^[18] proposed a hot water treatment in breaking hard seed mechanism for legumes. Therefore, the objective of the present study was to investigate effective methods of overcoming hard seededness dormancy for forage legume species and to determine the rate of hard seededness in forage legume species collected from natural rangeland.

MATERIALS AND METHODS

Seeds of forage legumes were handpicked from natural rangeland in the province of Samsun (41°21’ N, 36°15’ W, elevation 120 m) during July of 2002. Since flowering occurred over an extended period of time, all pods, which were either full or dry, were collected. After 6 months, under laboratory conditions, germination rates of the legumes were determined.

In this study, the seeds of 5 annual clovers (T. resupinatum, T. subterraneum, T. alexandrinum, T. meneghinianum and T. striatum), 3 medics (M. hispida, M. arabica and M. scutellata) and 2 perennial Medicago (M. lupulina and M. falcata) species were used.

Seed treatments consisted of the following: (1) mechanical disruption of seed coat by sandpaper (2) immersion in 0.18 mol L^-1 sulfuric acid for 30 sec., (3) immersion in 75°C water for 5 min, (4) immersion in 25 mg L^-1 gibberellic acid, (5) pre-heating at 40°C for 30 min, (6) pre-cooling at 3°C for 7 days and (7) an untreated control germinated in distilled water.

The treated seeds were placed in individual, sterilised petri dishes containing moisture-retaining paper liners. Paper liners in the petri dishes were kept moist throughout the germination period. Germination trials were conducted in a controlled environment germinator with 12 h light and dark cycles at a constant temperature of 25°C. Germinated seeds were counted at day 21 after the initiation of the germination trial. Germination was defined as the development of both a functional radical and at least 1 cotyledon. Germination percentages were transformed for statistical analysis (arcsine of square root of percent germination x 0.01) with the original data. The transformed data numbers were analysed according to design of randomised plots. Differences among each application were assessed according to LSD test (Level of significance p<0.01).