ABSTRACT: The root system architecture (RSA) of plants and its functioning play a fundamental role in a number of plant growth mechanisms including water and nutrient uptake. Optimization of the RSA is important for stable and increased plant productivity under adverse conditions. Despite its great importance, studying the RSA is notoriously laborious because of the difficulty of accessing the rooting system of plants. We developed a root phenotyping platform, PhenoRoots, which allows for the non-invasive study of plant RSA. The system was built using inexpensive material and was designed to provide medium throughput. Substrate or soil-filled rhizotrons are used to grow plantlets, whose roots are directly visible through a glass plate. An experiment conducted on a panel of twenty Upland cotton (Gossypium hirsutum L.) varieties demonstrated the usefulness of the platform in assessing RSA traits. A number of traits, destructive and non-destructive, related to the RSA were measured and statistically analyzed. The non-destructive traits based on image analysis of roots were more accurate and showed high correlation with the time-consuming destructive measurements. The platform allowed for capturing the phenotypic and genetic variability found in the panel of cotton varieties, and to define three contrasting RSA patterns. PhenoRoots provides an inexpensive alternative to the medium throughput analysis of RSA traits in plants.

RESUMO. Os cotonicultores do mundo inteiro sofrem com as perdas causadas pela presença de fitonematoides nas lavouras. Assim o objetivo deste trabalho foi estudar a herança da resistência do acesso TX 25 de Gossypium hirsutum raça punctatum a Meloidogyne incognita raça 3. Foram utilizados acessos de Gossypium sp. pertencentes ao Banco de Germoplasma da Embrapa Algodão. Foram realizados dois experimentos em dois anos consecutivos. No primeiro ano foram testados FiberMax 966 e TX 25 como parentais suscetível e resistente, respectivamente, e as gerações F1, F2 e retrocruzamento. No segundo experimento foram testados os parentais FiberMax 966 e TX 25, a geração F2 além dos genótipos M315 (resistente) LA887 e DeltaOpal (moderadamente resistentes). Em ambos experimentos as plantas foram inoculadas com 2000 ovos e J2 de M. incognita raça 3. As avaliações ocorreram aos 120 dias após a inoculação, e avaliou-se índice de galhas, índice de massa de ovos e fator de reprodução. No primeiro experimento as plantas da geração F1 e do retrocruzamento se mostraram suscetíveis, As plantas da geração F2 nos dois experimentos apresentaram uma proporção de três plantas resistentes para uma suscetível indicando resistência de caráter oligogênico.

ABSTRACT. Cotton producers worldwide suffer with the losses caused by the presence of phytonematodes. The aim of the present study was to investigate the inheritance of resistance to Meloidogyne incognita race 3 in Gossypium hirsutum variety punctatum accession TX 25. Accessions of Gossypium sp. were obtained from the germplasm bank of Embrapa Cotton. Two experiments were performed in two consecutive years. In the first experiment, a susceptible parental line, FiberMax 966, a resistant parental line, TX 25, and their F1, F2 and backcross generations were tested. In the second experiment, parental lines FiberMax 966 and TX 25, their F2 generation, and genotypes M315 (resistant), LA887 and DeltaOpal (moderately resistant) were tested. In both experiments, plants were inoculated with 2000 eggs and J2 of M. incognita race 3. The gall index, egg mass index and reproduction factor were evaluated 120 days following inoculation. In the first experiment, plants from the F1 and backcross generations were susceptible. Plants from the F2 generation presented a 3:1 resistant-to-susceptible ratio in the two experiments, indicating oligogenic resistance.

O objetivo deste trabalho foi caracterizar populações de Gossypium barbadense dos estados do Amapá e Pará. A caracterização in situ foi conduzida por meio de entrevistas com os proprietários das plantas e por observações sobre o ambiente. Tecidos de folhas ou de pétalas, além de sementes, foram coletados para a caracterização genética com marcadores SSR ("single sequence repeats") e para o armazenamento em bancos de germoplasma, respectivamente. As plantas eram mantidas em fundos de quintal e usadas, principalmente, para fins medicinais. As análises genéticas não mostraram plantas heterozigotas nos locos testados (f = 1), o que indica que a reprodução ocorre principalmente por meio de autofecundação. A diversidade genética total foi alta (He = 0,39), e um alto nível de diferenciação foi observado entre as plantas de algodoeiro dos dois estados (F ST = 0,36). Métodos convencionais para a manutenção in situ das populações de G. barbadense não são aplicáveis. A conservação da variabilidade genética das populações presentes nos dois estados deve ser realizada pela coleta de germoplasma e pela constituição de bancos de sementes ex situ.

The objective of this work was to characterize the populations of Gossypium barbadense in the states of Amapá and Pará, Brazil. In situ characterization was conducted through interviews with the owners of the plants and environmental observations. Leaf or petal tissue as well as seed samples were collected for genetic characterization by single sequence repeats markers and for storage in germplasm banks, respectively. The plants were maintained in dooryards and used mainly for medical purposes. The genetic analysis showed no heterozygous plants at the loci tested (f = 1), indicating that reproduction occurs mainly through selfing. The total genetic diversity was high (He = 0.39); and a high level of differentiation was observed between cotton plants from the two states (F ST = 0.36). Conventional methods of in situ maintenance of G. barbadense populations are not applicable. The conservation of the genetic variability of populations present in the two states could be achieved through germplasm collection and establishing of ex situ seed banks.