AbstractTwo irrigation experiments with cigar-filler tobacco were conducted on the Gurabo Substation Experimental Farm in a field graded for furrow irrigation. The objective was to evaluate the effect of different irrigation frequencies on the yield and quality of two tobacco varieties, P.R. 1-60 and a mosaic resistant line, X-13. Irrigation significantly increased the yield of varieties X-13 and P.R. 1-60. However, in spite that, the yield of P.R. 1-60 tobacco was greater under all treatments; the former showed about three times as much response to irrigation as compared with no irrigation. This variety (X-13) was also responsive to the irrigation level, in spite of light, but well-spaced precipitation between primings. A high incidence of mosaic on P.R. 1-60, which appeared since the fifth priming, probably masked a better response of this variety to irrigation. In an attempt to trace back to plant nutrition the injury caused by mosaic on P.R. 1-60 yields, a linear regression of yield on mineral content of the leaves was carried out, using the individual yield data by experimental units. From an analysis of these data, it seems likely that mosaic caused a yield-limiting effect on P.R. 1-60 as a result of adversely affecting the uptake of minerals by the plant. On the other hand, when observing the highly significant regression of X-13 yields on the moisture content of the leaves and at the same time comparing its regression coefficient (slope) with the corresponding one in variety P.R. 1-60, one may conclude that X-13 made a more efficient use of irrigation which was expressed in greater yield response.
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