Flower initiation in relation to maturity in crop plants. IV.* Sowing time and maturity type in pea (Pisum sativum L.) in Australia

Seven varieties of pea (Pisum sativum L.) sown monthly through the year in the temperate climate at Melbourne (38° S.), varied in their pattern of reproductive development according to their maturity type. The pattern was simple in the five early to mid-season varieties (Alaska, Collegian, Canner's Perfection, Dun, Partridge) in which rate was controlled directly by temperature, whereby the growing period after spring sowing was half that after winter sowing. The pattern was complex in the late varieties (Mackay, Austrian Winter) in which the slowest development followed sowing in late summer and early autumn. At each sowing, the range in time of flowering of early to late varieties resulted from a decreasing tendency to reach flower initiation from fast (Alaska) to very slow (Dun, Partridge, Mackay and Austrian Winter), together with an increasing positive sensitivity to photoperiod and a negative sensitivity to temperature. Both responses ranged from absent in Alaska to weak in Canners, Collegian and Dun, slightly more in Partridge and to strong in the two latest varieties. In Partridge, the sensitivity to photoperiod continued after flower initiation, causing abscission of flower buds in winter-sown plants. Three relationships can be used to forecast the ability of a variety to fit its seed maturity to a given growing season: the correlation between (1) early and later stages of development; (2) leaf stage at flower initiation and at first flower; (3) rate of development and temperature. Thus a sound basis for planning yield improvement is provided. _______________ *Part III, Aust. J. Agric. Res., 17: 1 (1966).