The objective is the development of inbred lines to get waxy endosperm hybrids suitable for the wet-milling process. Such hybrids would allow the extraction of modified starch useful for food industry, adhesives and others.

With this purpose during the summer of 1990-1991, a breeding program similar to the one proposed by Cornelius and Dudley (1974) was initiated. The basic germplasm used were four waxy endosperm maize populations (S0) called: SCV1, SCV2, WEM, and FW as well as two hard endosperm populations named CP27 and S80. In each population, couples of the best individuals were crossed, whilst some others were selfed, and free pollination was also allowed. This way, from each one of the original populations, two subpopulations were obtained as well as the first generation of selfings (S1) during the first year. These materials were agronomically evaluated during 1991-92 and then the second generation of selfings (S2) and the first generation of sib matings (SI1) was obtained. These materials, along with the S1's and S0's, were agronomically evaluated during the field crop 1992-93 for different plant and prolificacy traits. The plant traits measured were: plant height in meters (PH) - ear insertion height in meters (EIH) - number of tillers (NT) and number of leaves (NL). The prolificacy traits measured were: number of productive nodes (PN) - number of ears in the uppermost node (EUN) - number of ears per tiller (ET) and number of ears per plant (EP).

Tables 1 and 2 show the average values obtained for each trait in each generation as well as the relative values (in percentage) for each trait in the inbreeding generations referred to as the S0 generation average values. It is easily noticed that the average values decreased through the generations of inbreeding, though the speed of this process depends on both the nature of the original population and on the inbreeding method applied.

Table 1. Plant trait average values and relative values for the original populations and their derived inbred lines.
 

		PH (m)		EIH (m)		NT		NL
Generation		abs.	rel.	abs.	rel.	abs.	rel.	abs.	rel.
SCV1	(S0)	1.62	100.0	0.67	100.0	1.58	100.0	10.65	100.0
	(S1)	1.49	92.0	0.48	71.6	1.27	80.4	10.51	98.7
	(SI1)	1.53	94.4	0.63	94.0	1.38	87.3	10.85	101.9
SCV2	(S0)	1.40	100.0	0.43	100.0	1.14	100.0	10.32	100.0
	(S1)	1.19	85.0	0.39	90.7	1.08	94.7	9.61	93.1
WEM	(S0)	1.33	100.	0.33	100.0	1.42	100.0	10.17	100.0
	(S1)	1.26	94.7	0.25	75.7	1.26	88.7	9.78	96.2
	(SI1)	1.30	97.7	0.31	93.9	1.28	90.1	9.40	92.4
FW	(S0)	2.01	100.0	0.68	100.0	1.12	100.0	13.03	100.0
	(S1)	1.86	92.5	0.65	95.6	1.10	98.2	12.11	92.9
	(SI1)	1.92	95.5	0.69	101.5	1.05	93.7	11.00	84.4
CP27	(S0)	1.88	100.0	0.67	100.0	1.12	100.0	12.00	100.0
	(S1)	1.84	97.9	0.62	92.5	1.05	93.7	12.53	104.4
	(S2)	1.78	94.7	0.57	85.0	1.06	94.6	11.94	99.5
S80	(S0)	1.90	100.0	0.62	100.0	1.18	100.0	11.92	100.0
	(S1)	1.72	90.5	0.49	79.0	1.25	105.9	10.25	86.0
	(S2)	1.70	89.5	0.42	67.7	1.12	94.9	11.87	99.6

Table 2. Prolificity trait average values and relative values for the original populations and their derived inbred lines.
 

		PN		EUN		ET		EP
Generation		abs.	rel.	abs.	rel.	abs.	rel.	abs.	rel.
SCV1	(S0)	1.46	100.0	1.00	100.0	1.46	100.0	2.23	100.0
	(S1)	1.20	82.2	1.00	100.0	1.20	82.2	1.57	70.4
	(SI1)	1.19	81.5	1.00	100.0	1.19	81.5	1.61	72.2
SCV2	(S0)	1.14	100.0	1.00	100.0	1.14	100.0	1.27	100.0
	(S1)	1.27	111.4	1.00	100.0	1.27	111.4	1.35	106.3
WEM	(S0)	1.50	100.0	1.00	100.0	1.50	100.0	2.02	100.0
	(S1)	1.09	72.7	1.00	100.0	1.09	72.7	1.35	66.8
	(SI1)	1.48	98.7	1.00	100.0	1.48	98.7	1.86	92.0
FW	(S0)	1.25	100.0	1.00	100.0	1.25	100.0	1.37	100.0
	(S1)	1.04	83.2	1.00	100.0	1.04	83.2	1.14	83.2
	(SI1)	1.00	80.0	1.00	100.0	1.00	80.0	1.06	77.4
CP27	(S0)	1.53	100.0	1.14	100.0	1.53	100.0	1.71	100.0
	(S1)	1.43	93.5	1.00	87.7	1.43	93.5	1.47	86.0
	(S2)	1.37	89.5	1.00	87.7	1.37	89.5	1.44	84.2
S80	(S0)	1.22	100.0	1.06	100.0	1.22	100.0	1.37	100.0
	(S1)	1.17	95.9	1.08	101.9	1.17	95.9	1.35	98.5
	(S2)	1.08	88.5	1.00	94.3	1.08	88.5	1.25	91.2

Table 3 shows the potential yield estimated for the original populations and for the lines derived from them. This estimation resulted from relating the average weight of kernels/ear (in grams) with the number of ears per plant (EP) and the sowing density used (57,142 plants/hectare).

Table 3. Potential yield for the original populations and their derived inbred lines.
 

Generation		Kernel weight (g/ear)	EP	Yield (Kg/ha)
SCV1	(S0)	60.45	2.23	7,702
	(S1)	44.00	1.57	3,947
	(SI1)	55.88	1.61	5,140
SCV2	(S0)	57.40	1.27	4,165
	(S1)	48.70	1.35	3,756
WEM	(S0)	62.00	2.02	7,156
	(S1)	37.50	1.35	2,892
	(SI1)	59.43	1.86	6,316
FW	(S0)	133.00	1.37	10,411
	(S1)	80.00	1.14	5,211
	(SI1)	119.00	1.06	7,208
CP27	(S0)	92.29	1.71	9,018
	(S1)	91.84	1.47	7,714
	(S2)	80.62	1.44	6,634
S80	(S0)	76.07	1.37	5,955
	(S1)	65.08	1.35	5,020
	(S2)	58.64	1.25	4,188

Actually we have S1 lines (F:0.5 - Hr:0.5); S2 lines (F:0.75 - Hr:0.25) and SI1 lines (F:0.25 - Hr:0.75) from which we are obtaining new lines and generations by selfing.

The materials obtained to date showed low yield, by which they will be employed to obtain waxy endosperm inbred lines that later on could be used to incorporate the waxy gene (wx) into high yielding hard endosperm inbred lines using backcrosses. Finally the modified endosperm lines will be used to obtain high yielding waxy endosperm hybrids. 

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