Stalk rot resistance in Maksimir 3 synthetic maize population after four cycles of recurrent selection

Fusarium stalk rot (FSR) and anthracnose stalk rot (ASR), caused by Fusarium spp. and Colletotrichum graminicola (Ces.) G.W. Wils. respectively, are the two most important stalk diseases in maize which increase the incidence of stalk lodging and reduce grain yield. The aim of the present study was to (1) evaluate the effect of four cycles of recurrent selection in the Maksimir 3 Synthetic (M3S) maize population on ASR and FSR resistance and (2) to investigate the correlation among the different disease rating methods. The experiment included six M3S cycle populations per se and their test-crosses with a single cross hybrid. ASR resistance was estimated on artificially inoculated plant rows using three ratings (the number of infected internodes, the number of internodes rotten more than 75% and evaluation of outer stalk discoloration) whereas FSR resistance was estimated in artificially inoculated rows as well as in naturally inoculated rows by rating severity of disease symptoms on longitudinally cut stalks using the standard resistance scale. The results of the present study showed that four cycles of selection in the M3S maize population, conducted primarily for grain yield improvement, did not significantly affect its resistance to both ASR and FSR. Among the disease ratings a moderate positive correlation was found only between two ASR resistance ratings (the number of infected internodes and the number of internodes rotted more than 75%) in both population per se (r=0.49**) and population test-crosses (r=0.56**)

BREEDING MAIZE FOR RESISTANCE TO NORTHERN LEAF BLIGHT (Exserohilum turcicum Pass.)

Siva pjegavost lista kukuruza koju uzrokuje gljiva Exserohilum turcicum (Pass.) najvažnija je lisna bolest kukuruza u humidnom području. Prvi hibridi kukuruza u SAD-u bili su osjetljivi prema ovoj bolesti. Zbog toga je započet program oplemenjivanja na otpornost koji se pokazao vrlo uspješnim. Rabljena je poligenetska i monogenetska otpornost. Međutim nakon 15 godina široke i neprekidne uporabe monogenetske otpornosti u SAD-u dolazi do pojave novog patotipa Exserohilum turcicum, rase 2, koja je kasnije nazvana rasa 1 budući da protiv nje gen Ht 1 nije djelotvoran. Nova rasa se brzo raširila u Americi, a kasnije i u Hrvatskoj. U svrhu proučavanja otpornosti kukuruza prema rasi 1 Exserohilum turcicum posijan je 2008. godine pokus sa 75 linija različitog porijekla. Linije iz heterotične grupe BSSS su bile osjetljive prema rasi 1 Exserohilum turcicum s prosječnom ocjenom 3,0, dok su linije iz heterotične grupe Lancaster otporne s prosječnom ocjenom 2,0. U drugom pokusu 2012. godine ispitana je otpornost 25 linija kukuruza prema rasi 0 i rasi 1 s ciljem da se utvrdi koje su linije otporne prema obje rase Exserohilum turcicum. Linije Pa875, Bc210K, H102, Bc1411, Pa887P, H111 i H95 otporne su p rema obje rasi 0 i r asi 1 Exserohilum turcicum. Monogenetska otpornost prema rasi 1 unesena je u 4 linije kukuruza (A632, Bc31002, Bc703-19 i Bc14).Northern leaf blight, caused by the fungus Exserohilum turcicum (Pass.) is the most important leaf disease of maize in humid environments. The first maize hybrids in the United States were susceptible to this disease. Therefore, breeding program for resistance was initiated and proved to be very successful. Polygenic and monogenic resistance were used. However, after 15 years of continuous and extensive use of monogenic resistance in the United States occurrence of a new pathotype of E.turcicum. race 2 was reported, which was later named race 1, because Ht 1 gene was not effective against it. New race quickly spread throughout the United States, and later in Croatia. To study maize resistance to race 1 of E. turcicum a trial was planted with 75 lines of different origin in 2008. The lines from the BSSS heterotic group were susceptible to race 1 of Exserohilum turcicum with average rating 3,0, while the lines from the Lancaster heterotic group were resistant with average rating 2,0. In the second experiment in 2012., 25 maize lines were tsted for resistance to race 0 and race 1 to detect lines resistant to both races of Exserohilum turcicum. Lines Pa875, Bc210K, H102, Bc1411, Pa887P, H111 and H95 appear to be resistant to both race 0 and race 1 of Exserohilum turcicum. Monogenic otpornost resistance to race 1 was incorporated into four maize lines (A632, Bc31002, Bc703-19 i Bc14)

BREEDING MAIZE FOR RESISTANCE TO NORTHERN LEAF BLIGHT (Exserohilum turcicum Pass.)

Siva pjegavost lista kukuruza koju uzrokuje gljiva Exserohilum turcicum (Pass.) najvažnija je lisna bolest kukuruza u humidnom području. Prvi hibridi kukuruza u SAD-u bili su osjetljivi prema ovoj bolesti. Zbog toga je započet program oplemenjivanja na otpornost koji se pokazao vrlo uspješnim. Rabljena je poligenetska i monogenetska otpornost. Međutim nakon 15 godina široke i neprekidne uporabe monogenetske otpornosti u SAD-u dolazi do pojave novog patotipa Exserohilum turcicum, rase 2, koja je kasnije nazvana rasa 1 budući da protiv nje gen Ht 1 nije djelotvoran. Nova rasa se brzo raširila u Americi, a kasnije i u Hrvatskoj. U svrhu proučavanja otpornosti kukuruza prema rasi 1 Exserohilum turcicum posijan je 2008. godine pokus sa 75 linija različitog porijekla. Linije iz heterotične grupe BSSS su bile osjetljive prema rasi 1 Exserohilum turcicum s prosječnom ocjenom 3,0, dok su linije iz heterotične grupe Lancaster otporne s prosječnom ocjenom 2,0. U drugom pokusu 2012. godine ispitana je otpornost 25 linija kukuruza prema rasi 0 i rasi 1 s ciljem da se utvrdi koje su linije otporne prema obje rase Exserohilum turcicum. Linije Pa875, Bc210K, H102, Bc1411, Pa887P, H111 i H95 otporne su p rema obje rasi 0 i r asi 1 Exserohilum turcicum. Monogenetska otpornost prema rasi 1 unesena je u 4 linije kukuruza (A632, Bc31002, Bc703-19 i Bc14).Northern leaf blight, caused by the fungus Exserohilum turcicum (Pass.) is the most important leaf disease of maize in humid environments. The first maize hybrids in the United States were susceptible to this disease. Therefore, breeding program for resistance was initiated and proved to be very successful. Polygenic and monogenic resistance were used. However, after 15 years of continuous and extensive use of monogenic resistance in the United States occurrence of a new pathotype of E.turcicum. race 2 was reported, which was later named race 1, because Ht 1 gene was not effective against it. New race quickly spread throughout the United States, and later in Croatia. To study maize resistance to race 1 of E. turcicum a trial was planted with 75 lines of different origin in 2008. The lines from the BSSS heterotic group were susceptible to race 1 of Exserohilum turcicum with average rating 3,0, while the lines from the Lancaster heterotic group were resistant with average rating 2,0. In the second experiment in 2012., 25 maize lines were tsted for resistance to race 0 and race 1 to detect lines resistant to both races of Exserohilum turcicum. Lines Pa875, Bc210K, H102, Bc1411, Pa887P, H111 and H95 appear to be resistant to both race 0 and race 1 of Exserohilum turcicum. Monogenic otpornost resistance to race 1 was incorporated into four maize lines (A632, Bc31002, Bc703-19 i Bc14)

Population Genomics Provide Insights into the Global Genetic Structure of \u3ci\u3eColletotrichum graminicola\u3c/i\u3e, the Causal Agent of Maize Anthracnose

Understanding the genetic diversity and mechanisms underlying genetic variation in pathogen populations is crucial to the development of effective control strategies. We investigated the genetic diversity and reproductive biology of Colletotrichum graminicola isolates which infect maize by sequencing the genomes of 108 isolates collected from 14 countries using restriction site-associated DNA sequencing (RAD-seq) and wholegenome sequencing (WGS). Clustering analyses based on single-nucleotide polymorphisms revealed three genetic groups delimited by continental origin, compatible with short-dispersal of the pathogen and geographic subdivision. Intra- and intercontinental migration was observed between Europe and South America, likely associated with the movement of contaminated germplasm. Low clonality, evidence of genetic recombination, and high phenotypic diversity were detected. We show evidence that, although it is rare (possibly due to losses of sexual reproduction- and meiosis-associated genes) C. graminicola can undergo sexual recombination. Our results support the hypotheses that intra- and intercontinental pathogen migration and genetic recombination have great impacts on the C. graminicola population structure

Population Genomics Provide Insights into the Global Genetic Structure of Colletotrichum graminicola, the Causal Agent of Maize Anthracnose

Understanding the genetic diversity and mechanisms underlying genetic variation in pathogen populations is crucial to the development of effective control strategies. We investigated the genetic diversity and reproductive biology of Colletotrichum graminicola isolates which infect maize by sequencing the genomes of 108 isolates collected from 14 countries using restriction site-associated DNA sequencing (RAD-seq) and whole-genome sequencing (WGS). Clustering analyses based on single-nucleotide polymorphisms revealed three genetic groups delimited by continental origin, compatible with short-dispersal of the pathogen and geographic subdivision. Intra- and intercontinental migration was observed between Europe and South America, likely associated with the movement of contaminated germplasm. Low clonality, evidence of genetic recombination, and high phenotypic diversity were detected. We show evidence that, although it is rare (possibly due to losses of sexual reproduction- and meiosis-associated genes) C. graminicola can undergo sexual recombination. Our results support the hypotheses that intra- and intercontinental pathogen migration and genetic recombination have great impacts on the C. graminicola population structure. IMPORTANCE Plant pathogens cause significant reductions in yield and crop quality and cause enormous economic losses worldwide. Reducing these losses provides an obvious strategy to increase food production without further degrading natural ecosystems; however, this requires knowledge of the biology and evolution of the pathogens in agroecosystems. We employed a population genomics approach to investigate the genetic diversity and reproductive biology of the maize anthracnose pathogen (Colletotrichum graminicola) in 14 countries. We found that the populations are correlated with their geographical origin and that migration between countries is ongoing, possibly caused by the movement of infected plant material. This result has direct implications for disease management because migration can cause the movement of more virulent and/or fungicide-resistant genotypes. We conclude that genetic recombination is frequent (in contrast to the traditional view of C. graminicola being mainly asexual), which strongly impacts control measures and breeding programs aimed at controlling this disease.This research was supported by grants AGL2015-66362-R, RTI2018-093611-B-100, and PID2021-125349NB-100, funded by the Ministry of Science and Innovation (MCIN) of Spain AEI/10.13039/501100011033; and by grant SA165U13 funded by the Junta de Castilla y Léon. F.R. was supported by grant FJC2020-043351-I financed by MCIN/AEI /10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. R.B. was supported by the postdoctoral program of USAL (Program II). F.B.C.-F. was supported by grant BES-2016-078373, funded by MCIN/AEI/10.13039/501100011033. S.B. was supported by a fellowship program from the regional government of Castilla y León. W.B. was supported by a productivity fellowship from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 307855/2019-8). Genome sequencing was funded by the UNC Microbiome Core, which is funded in part by the Center for Gastrointestinal Biology and Disease (CGIBD P30 DK034987) and the UNC Nutrition Obesity Research Center (NORC P30 DK056350). P.D.E. was partially supported by the USDA National Institute of Food and Federal Appropriations under Project PEN04660 and accession no. 1016474.Peer reviewe

COMBINING ABILITY OF SOME NEW Bc MAIZE INBREDS

U dvogodišnjim poljskim pokusima na dvije lokacije ispitana je kombinacijska sposobnost sedam srodnih samooplodnih Bc linija kukuruza križanih s četiri testera (Bc252, F2, Bc16881, Rx370-811). Efekti opće kombinacijske sposobnosti (OKS) linija za svojstvo sadržaj vode u zrnu su bili opravdani u sva četiri pokusa, za prirod zrna u dva, a za broj poleglih i polomljenih biljaka u tri pokusa. Linija Bc21491 je imala najviše pozitivne efekte OKS za svojstvo priroda zrna, međutim najkasnija je s najvećim pozitivnim efektom OKS za sadržaj vode u zrnu kod berbe. Linije Bc01/84, Bc706-43 i Bc24331 su se pokazale kao rane s negativnim efektom OKS za sadžaj vode u zrnu kod berbe. Linije Bc24331, Bc01/84 i Bc706-9 su se na osnovi efekata OKS pokazale kao najotpornije prema lomu, dok su najbolji opći kombinatori za broj poleglih biljaka bile inbred linije Bc706-43, Bc706-9 i Bc24331. Specifična kombinacijska s posobnost je najznačajnija za svojstvo priroda zrna gdje su u tri pokusa dobiveni opravdani efekti SKS. Križanci Bc24331xBc16881, Bc24331xRx370-881, Bc406-87xF2 i Bc21491xBc252 su se istakli pozitivnim efektima SKS za prirod zrna. To su uz rani hibrid Bc706- 9xBc252 i gospodarski najvrednije kombinacije. Primijenjena shema linija x tester pokazala se djelotvornom u praktičnom oplemenjivanju kukuruza.Combining ability of seven related Bc maize inbreds, crossed with four testers (Bc252, F2, Bc16881, Rx370-811) was tested in two year field trials, at two locations. GCA effects of the lines were significant for grain moisture in all four trials, for grain yield in two trials, and for lodged and broken plants in three trials. The line Bc21491 had the highest positive GCA effects for grain yield. However, it was latest, with the highest positive GCA effect for harvest grain moisture. The lines Bc01/84, Bc706-43, and Bc24331 proved to be late with negative GCA effect for harvest grain moisture. Based on GCA effects, the lines Bc24331, Bc01/84 and Bc706-9 proved as most resistant to breakage. The best general combiners for number of lodged plants were the lines Bc706-43, and Bc706 and Bc24331. Specific combining ability was omst significant for grain yield. In three trials, SCA effects were significant. The crosses Bc24331 x Bc16881 ,Bc24331 x Rx370-811 , Bc406-87 x F2, and Bc21491 x Bc252 were distinguished by their positive SCA effects for grain yield. Along with the early hybrid Bc706-9 x Bc252, they are economically the most valuable combinations. The applied line x tester scheme proved to be effective in practical maize breeding