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Dep. Tropical Plant and Soil Science, College of Tropical Agriculture and Human Resources, Univ. of Hawaii, 3190 Maile Way, Honolulu, HI 96822. Institutional Sponsor: University of Hawaii
* Corresponding author (Brewbake{at}hawaii.edu).
ABSTRACT
Nine open-pollinated populations of maize (Zea mays L.), ‘HIC1’ (Reg. No. CV-2, PI 652866), ‘HIC2’ (Reg. No. CV-3, PI 652867), ‘HIC3’ (Reg. No. CV-4, PI 652868), ‘HIS1’ (Reg. No. CV-5, PI 652869), ‘HIS2’ (Reg. No. CV-6, PI 652870), ‘HIS3’ (Reg. No. CV-7, PI 652871), ‘HIS4’ (Reg. No. CV-8, PI 652872), ‘HIS5’ (Reg. No. CV-9, PI 652873), and ‘HIS6’ (Reg. No. CV-10, PI 652874), were released by Hawaii Foundation Seeds of the College of Tropical Agriculture and Human Resources of the University of Hawaii. Six are inbred-based synthetic populations (HIS1–HIS6) selected for resistance to specific diseases, and three are composites (HIC1–HIC3) derived from open-pollinated predecessors. The populations are largely tropically adapted flints that involve from 10 to 25% temperate parentage. They represent a total of 92 cycles of recurrent selection, and all are resistant to Maize mosaic virus.
Abbreviations: CTAHR, College of Tropical Agriculture and Human Resources • GCA, general combining ability • HFS, Hawaii Foundations Seeds • MMV, Maize mosaic virus
Nine open-pollinated populations of maize (Zea mays L.), ‘HIC1’ (Reg. No. CV-2, PI 652866), ‘HIC2’ (Reg. No. CV-3, PI 652867), ‘HIC3’ (Reg. No. CV-4, PI 652868), ‘HIS1’ (Reg. No. CV-5, PI 652869), ‘HIS2’ (Reg. No. CV-6, PI 652870), ‘HIS3’ (Reg. No. CV-7, PI 652871), ‘HIS4’ (Reg. No. CV-8, PI 652872), ‘HIS5’ (Reg. No. CV-9, PI 652873), and ‘HIS6’ (Reg. No. CV-10, PI 652874), have been released by Hawaii Foundation Seeds (HFS) of the College of Tropical Agriculture and Human Resources (CTAHR) of the University of Hawaii. Six are inbred-based synthetic populations (HIS1–HIS6) selected for resistance to specific diseases and three are composites (HIC1–HIC3) derived from open-pollinated predecessors. The populations are largely tropically adapted flints that involve from 10 to 25% temperate parentage and that represent a total of 92 cycles of recurrent selection. All were bred to be essentially homozygous for resistance to Maize mosaic virus (MMV), a major disease in tropical ecosystems (Brewbaker, 1979, 1981; Ming et al., 1997). This accompanies the series of conversions of 40 field corn inbreds to MMV resistance (Brewbaker, 1997; Brewbaker and Josue, 2007) and of many other field and sweet corns not formally released (Brewbaker et al., 1989). Table 1 summarizes the primary objectives of their selection.
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All populations were advanced through recurrent mass selection in fields of the Waimanalo Research Station on Oahu in Hawaii (20 m elevation, 24.5°C average annual temperature, 21°N latitude). Selected populations were advanced in fields of the Mealani Research Station on Hawaii Island (850 m elevation, 17°C average annual temperature). No fungicides or insecticides were applied to any of these fields. Selections for disease resistance were made before anthesis whenever possible. Breeding nurseries were planted in 295 of the 360 mo of their development. This afforded a type of shuttle breeding between the short-day, low-light, and high-disease conditions of winter and the high temperatures (mean 28°C) and insect pressures of summer (Brewbaker, 2003). Hawaii's congenial environmental conditions encouraged weekly observation and selection during emerging epibiotics. The author participated in the selection of all 92 of the populations.
Populations consisted of 2000 to 3000 hills planted at a density of 140,000 per hectare and later thinned to <70,000 per hectare. Most cycles of selection involved roguing by sickle twice before pollination and once at late sweet-corn stage. Minimally, 200 ears were harvested. Roguing for agronomic traits focused on brace-root formation, lodging resistance and ear position—traits in which tropical maize often rates poorly. Plants were selected for high leaf-area indices, dark plant coloration, early canopy closure and stay-green. Erect-leaf type was rare in these populations but favored where present.
All populations were selected under high pressure in Hawaii from kernel rot and seedling blight due to Fusarium verticillioides Sheld., and from the omnipresent MMV (Ming et al., 1997), common rust (Puccinia sorghi Schw.), and southern rust (Puccinia polysora Underw.). Other diseases common in the breeding nurseries included bacterial leaf blight [Acidovorax avenae (Manns) Willems, also known as Pseudomonas avenae Manns] and brown spot (Physoderma maidis Miyabe). Aflatoxin-inducing Aspergillus spp., common smut [Ustilago maydis (DC) Cda.], and maydis blight [Bipolaris maydis (Nisik.) Shoem.] were diseases rarely seen in Waimanalo and would not have been major factors in genetic advance under selection. Northern leaf blight [Exserohilum turcicum (Pass.) L&S] was also uncommon at Waimanalo but severe at the Mealani station, where most populations were evaluated.
Characteristics
Table 2 summarizes data for yields and heights of the nine populations under typical summer (high yield) conditions in Hawaii. Yields are of shelled grain, plant heights are to top of tassel, and ear heights are to base of uppermost ear. The two low-yielding composites involved teosinte parentage (HIC2) or were bred as an "Indian corn" (HIC3). All populations were similar in maturity in Hawaii with anthesis ranging from 58 to 68 d. For comparison B73 and Mo17 are 60-d inbreds at this location.
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HIS2: High-GCA Synthetic
HIS2 is a synthetic based on 18 inbreds with superior general combining ability (GCA), based on hybrids tested in Hawaii. Group A parents CIMMYT A21, CIMMYT T11, Hi33, Hi47, Hi49, ICAL221, INV534, and Ky226 were crossed in 1986 with Group B parents that included B77, CI66, CM103, H55, Hi26, Hi28, Hi29, Hi31, Hi34, and Hi65. Parentage was about 50% temperate, and performance should optimize in subtropical regions like Hawaii. Advanced through six cycles of recurrent selection, HIS2 has excellent form and agronomic traits in Hawaii. It is predominantly a yellow flint with 
5% white kernels.
HIS3: Southern Rust–Resistant Synthetic
HIS3 is an inbred-based synthetic developed with high general resistance of Southern rust. Our evaluations were made at Waimanalo Research Station on the Island of Oahu at sea level, where this disease is particularly severe every winter and none of the Rpp monogenes are effective. Inbred parents used for general resistance in 1985 on the basis of trials in Nigeria, the Philippines and Hawaii (Brewbaker et al., 1989) included CIMMYTT-11, Fla2AT115, Hi34, Hi66, ICAL210, ICAL219, ICAL223, INV138, INV534, Ki9, MIT2, Narino330, SC55, TZi10, TZi11, TZi12, TZi14, TZi15, and TZi30 (1 temperate, 18 tropical). The intercrossed population was advanced by recurrent mass selection for 10 cycles in Hawaii, with emphasis on improvement of agronomic traits. It is predominantly a yellow flint with 10% white kernels. Very high tolerance of the rust has been verified in disease nurseries in which susceptible temperate hybrids failed to produce grain, and it has proved outstanding in yield (Table 2).
HIS4: Common Rust–Resistant Synthetic
HIS4 is an inbred-based synthetic developed with high general resistance of common rust. Our evaluations were also made at Waimanalo Research Station, where this disease is particularly severe in late spring and where none of the Rp loci for racially specific resistance are effective (Kim and Brewbaker, 1977). Inbred parents chosen for general resistance in 1987 on the basis of trials in Nigeria and Hawaii (Brewbaker et al., 1989; Kim and Brewbaker, 1977) included B84, CIMMYT T11, CM118, Fla2AT115, Hi28, Hi32, Hi33, Hi34, Hi40, Hi41, Hi57, Hi58, ICA27, ICA219, ICA223, MIT2, Nariño 330, and Oh43 (5 temperate, 13 tropical). The intercrossed population was advanced by recurrent mass selection for nine cycles in Hawaii, with emphasis on improvement of agronomic traits. It is predominantly a yellow corn that ranges from hard flint to semident and that segregates 5% white kernels. High tolerance of the common rust races present in Hawaii has been verified in several disease nurseries, and it has been outstanding in yield (Table 2).
HIS5: Southern Blight–Resistant Synthetic
HIS5 is an inbred-based synthetic developed with high general resistance to Southern blight. This disease is not common in Hawaii, and our evaluations and selection of parent inbreds relied on collaborators in Cameroon, Mexico, Korea, India, and Nigeria (Brewbaker et al., 1989). Inbred parents chosen in 1987 for general resistance included Fla2AT114, Fla2AT115, Fla2AT116, Fla2BT73, Fla2BT106, Hi35, Hi39, Hi57, Hi58, ICAL221, INV534, TZi3, TZi5, and TZi11 (five temperate, nine tropical). The intercrossed population was advanced by recurrent mass selection for six cycles in Hawaii, with emphasis on improvement of agronomic traits. Kernels range from yellow to orange and from hard flint to semident.
HIS6: High-Performance Synthetic
HIS6 is a synthetic based on 38 yellow-kernelled inbreds with superior agronomic traits and hybrid performance in Hawaii. Evaluations of these parents and their hybrids were made at Waimanalo and at Mealani. The selected inbred parents were CML223, CML295, FW1, FW6, Hi26, Hi28, Hi34, Hi41, Hi42, Hi43, Hi44, Hi45, Hi46, Hi47, Hi49, Hi50, Hi51, Hi52, Hi53, Hi54, Hi56, Hi57, Hi58, Hi59, Hi60, Hi61, Hi62, Hi63, Hi64, Hi65, Hi66, Hi67, Hi68, KS23 (three sublines), MF6, and ZH1. Parentage thus included 10 temperate and 28 tropical inbreds. All were resistant to MMV and to other diseases common in our breeding nurseries (Brewbaker, 1997; Brewbaker and Josue, 2007). The intercrossed population has been advanced by recurrent mass selection for four cycles, in which two involved stratified sampling for ear weights.
HIC1: High-Lysine Composite
HIC1 is a composite homozygous for the high-lysine gene opaque-2 based on 18 cycles of breeding. The mutant was derived in 1967 from the Maize Genetic Coop's stock 65F-409-1/410-1 in a dent background. The genetic stock was crossed in Thailand with a Rockefeller Foundation o2 composite in a tropical flint background (Thai Comp x Colima Grp. I). Following two cycles of recurrent mass selection in Thailand, HIC1 was crossed with an o2 sister-line hybrid of B37 x H84 and subsequently backcrossed to HIC1. The genetic makeup thus is approximately 3/8 Thai composite, 3/8 genetic stock, and 2/8 B37/H84 (i.e., 3/8 tropical, 5/8 temperate), and it is yellow-kernelled. The Ht gene that we sought from H84 for tolerance of blight was subsequently overcome by racial variation of the pathogen. The population was then carried through 14 cycles of recurrent mass selection in Hawaii. Intensive selection was made for tolerance to kernel and ear rots due to Fusarium verticilliodes Sheld. that are severe on soft-kerneled floury genotypes. Two cycles involved seeds planted following selection on the basis of increased hard or vitreous endosperm. Most cycles of selection were grown under high insect pressure from earworms (Helicoverpa zea) and disease pressures from viruses and rusts.
HIC2: Zea diploperennis Introgressed Composite
HIC2 is a composite based on hybrids with perennial teosinte, Z. diploperennis, followed by five cycles of recurrent selection. Eleven corn inbreds (Hi25–Hi35) were crossed by Srinivasan (Srinivasan and Brewbaker, 1999a,b) with perennial teosinte as male parent. These highly tillered hybrids (average 5.4 tillers) were backcrossed by Srinivasan to the 11 parents (four temperate and seven tropical). The backcrosses were separated into A and B groups that were intercrossed in 1987 to establish the composite, which was then advanced by recurrent mass selection for five generations. The composite segregates widely for morphological traits (Srinivasan and Brewbaker, 1999a) and for ear traits (Srinivasan and Brewbaker, 1999b). It has been advanced without stringent selection for plant or ear type, and it is yellow kernelled and flinty. Tillering and flag-leaf development occur together in about 10% of the plants. HIC2 has not segregated perennial plants, which we surmise to be related to the fact that the population has the maize cytoplasm.
HIC3: "Indian-Corn" Composite
HIC3 is a composite with 24 cycles of breeding that was designed as a tropical "Indian corn" with an assortment of genes affecting plant and kernel color. A variegated-pericarp (p-vv) genetic stock was crossed with tropical inbred Hi27, and the hybrids were crossed with a temperate "Indian corn" composite of Dr. H.E. Brewbaker in 1969. Following three cycles of selection, the population was crossed to a tropical Hawaiian population with monogenic resistance to turcicum blight and common rust and then backcrossed four times selecting for rust and blight immunity. The monogenic immunities did not survive evolution of the pathogens in Hawaii, but the composite continued to be advanced for agronomic traits through 17 generations. The population was informally released to growers as "Kalakoa" (Hawaiian: "colorful," from "calico") in 1972 (Brewbaker, 1972). In 2002 it was crossed with variegated (p-vv) commercial popcorn, backcrossed twice, and advanced through three cycles of recurrent mass selection. The population is tall, ears are high, and kernels are flinty, and it does not have high tolerance of southern rust. Estimated phenotypic frequencies include 60% white endosperm, 15% red or purple aleurone, 10% variegated pericarp, 8% red pericarp, 5% bronze aleurone, 5% sugary-1 or brittle-1 endosperm, 2% purple plant, and 2% opaque-2 or floury-2 endosperm.
Availability
Foundation seed of these populations is available from Hawaii Foundation Seeds, Dep. of Tropical Plant and Soil Science, CTAHR, University of Hawaii, 3190 Maile Way, Honolulu, HI 96822.
Acknowledgments
The author acknowledges with thanks the assistance of many graduate students, post-doctorates and field staff at the Waimanalo and Mealani Research Stations in these conversions over the past four decades. Notable contributions have been made by Drs. Manuel Logroño, Aleksander Josue, Sarah Styan, Soon Kwon Kim, Myoung Hoon Lee, Hyeun Gui Moon, Yoonsup So, and Bingtian Wang.
Footnotes
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication July 8, 2008.
References
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