A Newly Bred ‘Gigas’ Form of Bread Wheat (<i>Triticum aestivum</i> L.): Morphological Features and Thermo‐photoperiodic Responses¹

Abstract

Individual segregants, as well as uniform F 6 to F 8 lines, originating from one group of spring wheat ( Triticum aestivum L.) crosses, had a series of striking characteristics setting them apart from the typical spring type. Tillering was limited, and in some lines nearly all of the plants were uniculms. Spikes were large and proliferous with maximum expression of 30 spikelets per ear, and 62.5 mg per kernel, and 12 florets and nine grains per spikelet have been recorded either in individual segregants or for certain lines. Vegetative parts were robust and vigorous, including broad, thick, dark green leaves, thick, stiff straw, and thick, large rachises, glumes and lemmas. Harvest index was higher than in a standard cultivar of regular growth habit. This complex set of characters typified plants of the new type only when grown in short (but increasing) day length and low temperature conditions (Mediterranean winters). Tests indicated a special thermo‐photoperiodic sensitivity in this material. Plants or lines included a wide spectrum of agronomic types with respect to plant height, size and quality of grains, and morphology of spikes and vegetative parts. The normal (2n = 42) chromosome complement of T. aestivum was found in 10 randomly sampled unicum plants.