436 



E. J. WELLHAUSEN 



mined in the same experiment under the same conditions. In calculating the 

 yield of the F2 generation, however, the average yield of the four parental 

 lines was estimated as 70 per cent of Mex. 39. In view of the fact that the Si 

 lines involved were the most vigorous within their respective varieties, this 

 estimation is conservative. Actual yields of the F2 generation in comparison 

 with Mex. 39 and the double cross hybrid are not yet available. 



Results in Zone 3 



Zone 3 comprises the corn belt of Mexico and produces more commercial 

 corn than any other area. In the eastern part of Zone 3, an area commonly 

 referred to as the Bajio, the race Celaya (Fig. 27.2) is widely distributed 



TABLE 27.6 



YIELD AND PER CENT DRY MATTER OF A DOUBLE CROSS 



HYBRID COMPARED TO THE OPEN-POLLINATED 



VARIETY MEX. 39 AND TO ITS F. YIELD* 



Hybrid 



(LI 27 X LI 193) X Mex. 39-26 X Mex. 39 



Comp. 1 



Mex. 39 O.P. (check) 



Av. of all possible singles 



Av. of parental lines (est. 70% of check) . . 

 F2 (calculated by Wright's formula) 



Yield in 

 % of 

 Check 



148 



100 



136 



70 



120 



* Calculated from average yield of the three inbreds and one composite and their 

 six possible single crosses. 



and is apparently a recent introduction into the area. The predominating 

 corn in the Bajio area at one time must have been the race Conico Norteno. 

 But as the root rot organism populations built up, the varieties of Conico 

 Norteno rapidly dropped in yield because of their almost complete root rot 

 susceptibility. Celaya probably originated in the State of San Luis Potosi 

 which is adjacent to the Bajio, but at a lower elevation than is common in 

 Zone 3. When introduced into the Bajio, it was a late variety and was first 

 grown only by farmers who had irrigation and could plant corn considerably 

 ahead of the rainy season. As irrigation farming increased, the race Celaya 

 became very popular and widespread. Selection pressure operated in the 

 direction of earliness, and certain varieties were developed which were more 

 productive than Conico Norteno on the better soils and under conditions of 

 a normal rainy season. The rainy season begins about July 1 and ends in 

 October. 



In the western part of Zone 3, the predominating types are varieties of 

 the race Tabloncillo and inter-mixtures of Tabloncillo, Celaya, and a third 



