Response of kernel growth of barley genotypes with different row type to climatic factors before and after inflection point of grain filling

Changes in patterns of rainfall and rising temperatures during grain development have already negatively affected yield gains of temperate cereals. This article reports on barley field trials with 15 two- and 10 six-row barley genotypes evaluated in eight environments where terminal drought was simulated by leaf defoliation applied seven days after heading. The experimental years were contrasting in terms of temperatures during grain filling. The focus of the study was to determine which barley type was more sensitive to terminal drought and high temperatures. The grain filling period was divided in two sub-periods: before (P1) and after (P2) inflection point (IP) of the growth curve, which occurs at the instant when the rate of accumulation ceases to accelerate and begins to slow down. For each period, climatic factors were calculated and their effects on the mean kernel growth rate (RG) were analyzed. To explore genotype x environment interactions for production per spike (PPS), the regression approach was adopted using climatic data in P1 and P2 as explanatory variables. Two-row barley had a significantly longer IP than six-row barley. IP was in a negative relationship with RG and PPS in both barley types. Six-row barley showed higher RG sensibility than two-row barley to drought stress during the period of the extensive kernel growth (P1). The number of days with moderately high (between 25 and 30 degrees C) and high (over 30 degrees C) temperatures had a higher negative effect on RG of two-row barley than six-row barley, particularly in P2. On the other hand, minimum temperatures were more negative for RG of the six-row barley than two-row barley, particularly under control conditions. In general, two-row barley showed better adaptation to low yielding environments, while six-row barley was more responsive to high yielding environments