Maize Genetics Cooperation Newsletter vol 84 2010

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of authors.

HONOLULU, HAWAII

University of Hawaii

Narrow Leaf 3 (nl3) on Chromosome 1.

----James L. Brewbaker

Narrow leaves occur in several maize mutants as pleiotropic effects (e.g., Corngrass, Ragged) but only two loci have been labeled �narrow leaf� and these are rather gross dwarfs. �Narrow leaf 3� is proposed here to designate near-isogenic lines we�ve developed that have a reduced leaf width compared to parent Hi27 but are otherwise quite normal.

Our Hawaii Foundation Seeds assemblage of near-isogenic lines (NILs) based on tropical inbred Hi27 currently includes about 150 genotypes (MNL81:15). These are now summarized on our website www.ctahr.hawaii.edu/hfs. All genes have been accessed from temperate-adapted inbreds or hybrids of the Maize Genetics Coop. Our initial crosses of the temperate lines with Colombian flint-derived Hi27 resulted in very impressive heterosis for all quantitative traits we measured. We�ve also encountered impressive heterosis among our own 6-BC NILs (MNL81:16). We have thus sought evidence for quantitative trait loci (QTLs) that are linked to the mapped mutant loci we�re transferring. .

. The narrow-leaf trait was observed in conversions of the pericarp and cob color locus P (Chrom. 1S-68.5). This locus is represented by allele p-ww in parent Hi27 which has no color in pericarp or cob. The conversion of Hi27 to p-rw (red pericarp, white cob) began in 1967 with MGC stock 63-2656-3/2655-5 (a Dt et lg2), a bronze-pericarp stock that was found also to carry p-rw. When selfing was initiated after 8 backcrosses (BCs) to produce homozygous red-pericarp lines, the narrow-leaf trait segregated as a simple recessive.

Two NILs are now maintained, nl3^Hi27 and (nl3 p-rw)^Hi27, the latter a double mutant with the red pericarp allele. Each conversion represents the 8 BCs and many sibs or selfs over more than 30 cycles of breeding. The narrow-leaf NILs are otherwise indistinguishable from Hi27 in leaf length, plant height, maturity, ear traits or in yield. The nl3 locus must be closely linked to the P locus. Also derived from this P locus stock were NILs of the double-cob mutant dbcb we reported last year in MNL83, all of which have normal leaf widths.

The nl3 trait is quite distinct from those described in the literature. Emerson�s locus nl1 on Chrom. 10S was a very weak mutant with linear leaf stripes resembling the gene lineate, also on 10. The lineate stripes in our stocks li^Hi27 and (g li)^Hi27 are in leaves of normal width, and stripes occur only along the veins, resembling symptoms of Maize Mosaic Virus. Neuffer�s nl2 on 5S-62 was described also as weak and irregular (formerly called �ragged�), and the gene acted as a dominant. Similarly, the EMS-induced mutant nl*-1517 was reported by Scanlon and Freeling (MNL70:15) to have shortened, narrow leaves with blades occasionally missing altogether and to be on Chrom. 3. Neuffer also reported nld (narrow-leaf dwarf), a small compact plant with narrow, rolled, chlorotic leaves. Among the 120+ genes represented in Hi27 NILs only Cg (corngrass) and Rg (ragged) have consistently narrower leaves than the parent. The leaves on tillers are often quite narrow, of course, as in our NILs for gt, tb and tlr (cf. our photo in MNL81:15), and many diseases and abiotic stresses can affect leaf length and width. Most mutants with shortened leaves (d1, na1, na2, py) have either normal or somewhat wider leaves.

The nl3 phenotype was most obvious among young plants (30-45 days) that also have a somewhat erect habit, not unlike our NILs for gs1 and gs2. The data in Table 1 were taken in the middle of first fully expanded leaves at 35 days after planting (about meiosis). Grand growth was just beginning (anthesis occurred 30 days later). The nl3 plants had leaves reduced in width by 9 mm without change in vein numbers on each side of the midrib. Hi27 was almost identical in these traits to Mark Zuber�s classic inbred Mo17. Contrasting data are presented in the table for dwarf d1^Hi27 with its highly expanded leaf blades with 11 veins on each side.

Table 1. Seedling leaf widths (mm) of nl3 mutants vs. Hi27 and d1

Line Width CV Veins

nl3 46.4 7.2% 8

Hi27 55.3 7.9% 8

d1 76.2 9.7% 11

Figure 1 shows Hi27 (center) and NILs nl3^Hi27 (left) and d1^Hi27 (right), a photo taken 43 days after planting and 23 days before anthesis.

Figure 1. Leaves of nl3^Hi27, Hi27 and d1^Hi27 (from left to right)

Complementary studies at anthesis included measurements over several years of the uppermost leaves and of leaves subtending the ear. These comparisons showed leaves of nl3 to average about 10% narrower than normal throughout their length without variation in vein number. The data are summarized in Table 2, again representing mid-leaf section. The data were also characterized by very low variances (CVs of 5.6% for ear leaf and 9.1% for uppermost).

Table 2. Mature leaf widths (mm) of nl3 mutants and inbred Hi27

Line Ear leaf Uppermost leaf

nl3 76.7 54.4

Hi27 86.0 65.3

Conversions of Hi27 from other sources to alleles p-vv, p-wr and p-rr did not segregate narrow leaf. There has been no evidence in our (nl3 p-rw)^Hi27 stock of mutability for the P locus. Both lines have always been characterized by reddish anthers, as contrasted with the bronze anthers of parent Hi27. Red anthers also occur in four of our NILs having red cobs due to allele p-wr. However, neither of the narrow-leaf NILs ever showed red cobs.

Variation in leaf length is a common pleiotropic trait with our dwarfing loci d1, na1, na2 and py. However, only the d1 locus (3S-30) has especially wide leaves with high vein number throughout development (Table 1, Figure 1). Our d1^Hi27 NIL also has a closely-linked locus conferring high susceptibility to southern rust, unique among Hi27 NILs that are routinely highly tolerant.