Josué Maldonado Ferreira

Chromosomal doubling of haploids, through exposure to antimitotic agents for specific periods, is crucial for obtaining doubled haploids. The objectives of this study were (a) to determine the potential for chromosome doubling by immersing the roots of haploid super sweet corn ( Zea mays L. var. saccharata ) seedlings at 17°C in solutions of colchicine, pronamide, and amiprophos‐methyl + pronamide for different exposure times; and (b) to compare the doubling effectiveness of these antimitotic solutions, for different exposure times at greenhouse and field cultivation. Putative haploid seeds from eight super sweet populations, obtained by crossing with the hybrid inducer CIM2GTAIL‐P1 × CIM2GTAIL‐P2, were used. The first experiment used exposure times of 5–12 h for colchicine and pronamide solutions and 5–16 h for amiprophos‐methyl at 17°C. In the second experiment, exposure times of 5, 6, and 7 h were chosen for pronamide and amiprophos‐methyl solutions, and 10, 11, and 12 h for colchicine, at 17°C. The hybrid inducer promoted a mean real haploid induction rate of 9.7%. Greenhouse treatments promoted greater success in obtaining doubled haploids. The pronamide solution led to greater lethality of seedlings but obtained mean overall success rates of 11.2%–12.7%, not differing from treatments using a solution containing amiprophos‐methyl. Colchicine treatment with 10 h of exposure at 17°C resulted in the best performance, with overall success rates of 32.3% in the greenhouse and 20.3% in the field, making it the best treatment for obtaining DHs in super sweet corn.

Doubled haploid technology accelerates the development of fully homozygous maize lines compared with conventional selfing. However, specific protocols for supersweet corn ( Zea mays L . var. saccharata ), particularly regarding immersion time in antimitotic solutions and temperature during chromosome doubling, remain poorly defined. This study investigated haploid induction rates in supersweet corn with a tropicalised haploid inducer hybrid and evaluated the effects of temperature and immersion time across three antimitotic solutions in an adapted newly germinated seeds method for chromosome doubling. Survival rate was assessed in diploid seeds immersed in water at 0°C, 17°C and 25°C and in haploid seeds treated with water at 0°C and 17°C, as well as with colchicine, pronamide and amiprophos‐methyl combined with pronamide, at 17°C under different immersion durations. Chromosome doubling efficiency of putative haploid was compared among the newly germinated seed treatments and with the root immersion method in colchicine. The tropical inducer hybrid showed an average haploid induction rate of 14.6%. Temperature and exposure time strongly affected survival and overall protocol feasibility, and 17°C emerged as the most suitable temperature by enabling longer exposure to antimitotic agents while maintaining higher survival. Treatments with 10 h in pronamide and 12 h in amiprophos‐methyl plus pronamide increased chromosome doubling but caused high mortality, indicating that shorter exposures are more suitable. Water treatment at 0°C did not improve chromosome doubling efficiency. These results demonstrate that herbicide‐based immersion of newly germinated seeds at 17°C is a promising alternative for chromosome doubling in tropical supersweet corn.

Colchicine is a widely used and effective agent for producing doubled haploid inbred lines in maize. However, its high toxicity and cost have prompted the search for safer and more economical alternatives for chromosome doubling. This study aimed to evaluate the effectiveness of pronamide and amiprophos‐methyl solutions as alternatives to colchicine for chromosome doubling in tropical white corn (Zea mays L.), to identify the potential for spontaneous chromosomal doubling in tropical white maize populations, and to compare the haploid induction rates of three tropicalized inducer lines (CIM2GTAIL‐P1, CIM2GTAIL‐P2, and CIM2GTAIL‐P3) along with their three hybrid combinations in crosses with tropical white corn. Eight populations of white corn were pollinated by six inducer genotypes, and the haploid induction rates were estimated. At the V2 stage, the roots of the haploid seedlings were washed and immersed in four treatments for chromosome doubling: a negative control with water, an amiprofos‐methyl and pronamide solution, a colchicine solution, and a pronamide solution. Parameters such as self‐pollination rate, self‐pollination efficiency, survival, reproduction, and overall success were estimated. The amiprofos‐methyl and pronamide treatment proved to be an effective alternative for the production of doubled haploid lines in tropical white corn, successfully replacing the use of colchicine. The tropical white corn populations presented spontaneous chromosome doubling rates ranging from 7.9% to 38.3%. The CIM2GTAIL‐P1 × CIM2GTAIL‐P2 hybrid demonstrated the highest haploid induction rate, with an average of 12.9%.

The double-haploid technology in maize was developed in temperate environments, using germplasm and inducers adapted for these environments, with the aim of accelerating the obtaining of homozygous inbred lines. Therefore, to advance this technology in tropical environments, research involving germplasm and inducers adapted for this environment is necessary. The objectives were to determine the haploidy induction rate in tropical common and supersweet corn populations, employing a tropicalized gymnogenetic inducer population, and to identify the effectiveness of chromosome doubling by colchicine injection. The haploidy inducer PI4003 was used as a male parent and crossed with 25 tropical maize populations (23 common and two supersweet). The putative haploid seeds, classified by the R1-nj gene marker, were sown in trays with peat during the 2020/21 and 2021/22 harvest seasons, and 100 µL of a solution of 0.125% colchicine and 0.5% dimethyl sulfoxide was injected into each haploid seedling at the V2 stage. The next day, the treated seedlings were transplanted to an irrigated field. The PI4003 inducer presented a haploidy induction rate ranging from 0.9% to 5%. There were significant differences to tropical genotypes and harvests for survival rates, reproduction rates, and overall success rates. The overall success rate ranged from 2.9% to 34%. The chromosome doubling method by colchicine injection proved to be effective, with lower colchicine consumption per haploid seedling treated and a reduction in the generation of toxic waste for disposal.

A produção de milho superdoce brasileira é preponderantemente destinada as indústrias de conservas, que necessitam de elevada produtividade, uniformidade e qualidade de produção, oferecidas pelas cultivares híbridas de linhagens. A tecnologia duplo-haploide (DH) está sendo utilizada para reduzir o tempo de produção de linhagens completamente homozigotas e melhor explorar a heterose em combinações híbridas em milho comum, mas ainda pouco estudada em milho superdoce. Os objetivos foram determinar o potencial de linhagens DHs de milho superdoce na síntese de híbridos; identificar linhagens DHs elites para uso como testadoras em cruzamento top crosses; determinar o tipo predominante de ação gênica para características importantes no melhoramento de milho superdoce e suas correlações. As 29 combinações entre linhagens DHs de quatro populações superdoce e seis testemunhas foram avaliadas na Fazenda Escola/UEL, durante as safras 2019/2020 e 2020/2021, empregando o delineamento de blocos casualizados, com 3 repetições. As características avaliadas foram: produtividades de espigas com e sem palha, produtividadede grãos; alturas de plantas e de espigas; comprimento e diâmetro de espigas; número de fileiras de grãos nas espigas; padrão agronômico e grau Brix. Houve efeito significativo de safras todas as características, sendo a safra 2020/2021 a melhor para produtividade. A interação tratamento x safra foi observada apenas para diâmetro de espiga e padrão agronômico. Na média das duas safras, 38% dos híbridos do dialelo foram superiores em relação às testemunhas comerciais, que ficaram agrupadas junto à média do restante dos híbridos avaliados. As linhagens L1 e L5 apresentaram as maiores estimativas de capacidade geral de combinação para as características de produtividades de espigas com palha, sem palha e de grãos, com valores iguais a 2244 e 2627; 1260 e 1388; 811 e 1000 kg ha-1, respectivamente, sendo candidatas para uso como testadoras em trabalhos futuros. Entre os híbridos mais produtivos, as maiores estimativas de capacidade específica para produtividades de espigas com palha, sem palha e de grãos foram observadas para os híbridos HA5, HB2 e HC12, com valores entre 4685 e 1947, 2829 e 1329, 1680 e 1095 kg ha-1, respectivamente. Foi verificado que as ações gênicas aditivas e não aditivas foram importantes para a maioria das características avaliadas. A característica produtividade de espigas sem palha é a que mais se correlaciona com produtividade de grãos, podendo ser utilizada para a seleção de genótipos mais produtivos para a produção de milho em conserva.

Knowledge about pests is essential for agriculture, as they can cause significant damage to crops. However, it is equally important to understand the natural enemies that assist farmers in controlling pest insect populations, thereby reducing the need for inputs and promoting production sustainability. The ability to recognize and identify natural enemies is even more relevant for producers who employ environmentally friendly and agroecological-based management techniques, such as biological pest control. Thus, the objective of this study was to assess the level of knowledge of organic and agroecological transition farmers in northern Paraná, Brazil, regarding the identification of pests and natural enemies, aiming to understand how the socioeconomic profile of the respondents influences their understanding of the ecological relationships between insects in the agroecosystem. To this end, a survey-type research was conducted in which 41 organic or agroecological transition farmers were interviewed in person. Farmers, in general, were able to recognize and identify pests in their crops however, they did not achieve the same success regarding natural enemies, highlighting their lack of awareness of the ecological role of this group of insects in the context of integrated pest management. It was observed that the species with the highest identification accuracies were: Aphis gossypii (100%), Bemisia tabaci (100%), Tuta absoluta (97.6%), Frankliniella sp. (95.1%), and Agrotis ípsilon (92.7%), all categorized as pests. On the other hand, the species with the lowest identification accuracies were: Lebia concinna (53.7%), Callida sp. (53.7%), Allograpta sp. (36.6%), Orius spp. (19.5%), and the bug from the Reduviidae family (17.1%), all belonging to the natural enemies group. It is evident that technical assistance and rural extension actions should focus on training and educating farmers dedicated to organic production about biological control management through the conservation and creation of habitats for natural enemies on their properties.

Water deficit (WD) promotes great losses in agriculture, and the development of new sustainable technologies to mitigate the effects of this stress on plants is essential. This study aimed to evaluate the morphophysiological and biochemical alterations induced by the priming of tomato seeds with different formulations in plants under field capacity and WD conditions. In the first experiment, the treatments consisted of nanoparticles of alginate/chitosan and chitosan/tripolyphosphate containing gibberellic acid (GA₃) in different concentrations (0.5, 5, and 50 µg mL⁻¹ GA₃), in addition to control with deionized water. The alginate/chitosan (5 µg mL⁻¹ GA₃) provided the greatest gains in plant growth under field capacity. In addition, under WD this treatment reduced damage to photosystem II (−14%), stomatal conductance (−13%), and water loss (−38%) and increased the instantaneous carboxylation efficiency (+24%) and intrinsic water use efficiency (+12%). In the second experiment, the treatments were alginate/chitosan nanoparticles containing GA₃ (NPGA₃ 5 µg mL⁻¹), free GA₃ (GA₃ 5 µg mL⁻¹), nanoparticles without GA₃ (NP), deionized water (WATER), and non-primed seeds (CONT). Under WD, GA₃ and CONT maintained plant growth and lost water rapidly, reducing stomatal conductance (−87%) and net photosynthesis (−69%). In contrast, NPGA₃ decreased leaf area (−44%) and increased root-to-shoot ratio (+39%) when compared to GA₃, reducing water loss (−28%). Activation of protective mechanisms (e.g., superoxide dismutase and catalase activities) by WATER, NPGA₃, and NP treatments also resulted in lower susceptibility to WD compared to CONT and GA₃. The results highlight the positive effect of seed priming on plant response to WD, which was enhanced by the use of nanoencapsulated GA₃.

Identification of early haploids is necessary to increase the efficiency of the double haploid production. The objectives were to determine the effectiveness of early selection of haploid seedling and to investigate the haploid inducers and donor tropical supersweet corn interactions, based on stomatal guard cell length. Two haploid inducers, three supersweet corn populations and its six combinations of F₁'s diploid and haploid, classified based on the expression of the R1-navajo gene and by the colors of the first leaf sheath in seedlings at the V2 stage, were used. From each seedling of the treatments, external epidermal impressions were taken to measure the stomatal guard cell length. F₁ haploids showed a 32.7% to 38.2% reduction in guard cell length compared to F₁ diploids. The parents contributed differently to reduce or increase guard cell length in the F₁'s combinations, but without specific interactions between parents.

Recurrent selection method was applied in one maize landrace (Zea mays L.) population, Macaco, for one cycle of selection. In the present study the changes in genetic structure were investigated at 18 microsatellite loci. A total of 81 alleles were observed in cycle 0 (C0) population which 79 were maintained in cycle 1 (C1) population. Thus, a reduction of 2.5% in the allele frequency was observed after one cycle of selection in C1 population. The heterozygozity reduction was also observed after one cycle of selection. In nearly 44% and 55% of the loci evaluated in C0 and C1 populations, respectivelly, the changes in allelic frequencies in populations were not due exclusively by genetic drift effects. Although few changes have been observed in allelic frequencies, the grain yield increase was observed after one cycle of recurrent selection. The genetic differentiation estimated by GST and RST values, for microsatellite data between C0 and C1 populations indicate that genetic variability degree was maintained in C1 population. This result suggest that C1 population can be used in a new recurrent selection cycles.

A proposta do Cruzamento Dialelo Parcial Circulante Interpopulacional (CDPCI) foi desenvolvida com a finalidade de explorar melhor a heterose, ao combinar linhagens de diferentes grupos heteróticos, e viabilizar a avaliação do potencial combinatório de um maior número de linhagens (n), que participam em s cruzamentos, com um número reduzido de combinações híbridos avaliadas (ns), com a possibilidade de estimação de [n(n-s)] híbridos não avaliados. Os objetivos foram determinar o potencial do CDPCI para identificar linhagens elites e combinações superiores nos híbridos avaliados e predizer o desempenho dos híbridos não avaliados, por meio de um modelo reduzido. Foram obtidos quatro dialelos CDPCI’s, envolvendo seis sintéticos de milho, empregando grupos de 20 linhagens S₅ por sintético, sendo cada linhagem combinada com quatro linhagens do grupo contrastante (s=4), em cada dialelo, dando um total de 80 combinações híbridas por dialelo, utilizadas para predição do desempenho de 320 outras combinações não avaliadas. As 80 combinações híbridas e quatro testemunhas comerciais foram avaliados para produtividade de grãos, utilizando o delineamento de blocos casualizados com duas repetições, em duas safras. As análises de variâncias individuais e conjuntas foram realizadas com base nas médias de tratamentos, sendo as análises dialélicas e estimativas de efeitos dos parâmetros genéticos realizadas pelo método dos quadrados mínimos ordinários. Os efeitos significativos de capacidade geral e específica de combinação e suas interações com safras, mostram que tanto os efeitos aditivos quanto de dominância foram importantes para a produtividade. Os modelos reduzidos para estimação de médias de híbridos tiveram elevada correlação com as médias observadas, com estimativas entre 0,75 e 0,93. O emprego do CDPCI’s é eficiente para predição dos híbridos não avaliados nos dialelos e permite identificar linhagens elites para síntese de híbridos.