3.4. Effects of growing conditions in season 1 on bud fertility in season 2
3.4.1. Evidence for a critical period just after grapevine flowering in season 1
Assuming that grapevine water status influenced bud fertility during specific periods of sensitivity during inflorescence development, we regressed bud fertility on FTSW for various hypothetical time periods (Fig. 1A). The maximum value of r2 was reached during the 500–600◦Cd period after bud burst in season 1 (r2= 0.7), the p-value being the most significant at the same time (p = 0.005). At that time in season 1, FTSW reduced bud fertility in season 2 (Fig. 1B). Although this period appeared to be the most critical one, the preceding and succeeding periods were also sensitive, and a general sensitive period could be defined from 400 to 700◦Cdafter budburst. This was confirmed by the fact that bud fertility in season 2 was well and better correlated with LNC and predawn at flowering in season 1 (Fig. 2A and B) than at flowering in season 2(Fig. 2E and F). This holds true for both cultivars in Experiments 1 and 2
3.4.2. Bud fertility in season 2 may be reduced by up to 40% by grapevine water and nitrogen status at flowering in season 1For both cultivars, inverse relationships were found between bud fertility in season 2 and LNC and predawn at flowering in season 1 (Fig. 2A and B). For Shiraz, bud fertility ranged between 1.31 and2.05: a decrease in LNC or predawn at flowering in season 1 might reduce bud fertility in season 2 by up to 36%. This reduction could reach 40% for Aranel as its bud fertility ranged from 1.34 to 2.21.
3.4.3. Water or nitrogen: which is the more limiting factor? Shiraz and Aranel displayed important differences with respect to the effects of water and nitrogen on bud fertility (Fig. 3).For Aranel the grapevine nitrogen status at flowering of season 1 explained most (60%) of the variation in season 2 bud fertility, whereas for Shiraz the water status at flowering in season 1 explained most (50%) of the variation in season 2 bud fertility.3.5. Effects of growing conditions in season 1 on berry number per bunch in season 23.5.1. Evidence for a critical period just after grapevine flowering in season 1 The analysis of various possible time periods for the effects of FTSW on berry number per bunch revealed a sensitive period from 400 to 700◦Cd after bud burst in season 1 with a critical period between 500 and 600◦Cd (Fig. 1B) during which the maxi-mum value of r2(r2= 0.54) and the lowest p-value (p = 0.024) were reached (Fig. 1D). As for bud fertility, relationships between berry number per bunch of season 2 and LNC and predawn were better when LNC and predawn were measured at flowering of season 1 than at flowering of season 2 (Fig. 2E and F). And this holds true for both cultivars in the two experiments.