A comparison of leaf appearance rates among teosinte, maize landraces and modern maize

The rate at which successive new leaves emerge at the stem apex in gramineae (phyllochron) is largely controlled by temperature. Utilizing genetic variation for the phyllochron may be a way to alter plants' responses to the environment or to manipulate time to maturity. Little is known about possible genetic variation in the phyllochron among maize landraces, its ancestor teosinte and modern maize. Controlled environment (phytotron) and field studies were conducted to investigate possible genetic variation for the phyllochron among seven maize (Zea mays) landraces (Apachito, Chapalote, Conico, Tabloncillo, Tehua, Tuxpeno, and Zapalote Chico) sampled from the center of maize diversity in Mexico, a modern US maize hybrid (B73 x Mo17), and two teosintes (Zea diploperennis and Z. mays ssp. parviglumis). In the phytotron the phyllochron was determined for three day/night temperature regimes (22/18, 27/21 and 33/25�C) under a 12 h photoperiod. Genetic variation for the phyllochron among the genotypes was observed in the phytotron and field, however, it was small with extreme values of about +/-15% of the mean. A generally similar phyllochron for modern maize and its wild relatives suggested that this trait has been conserved despite thousands of years of human and natural selection. A similar leaf development rate among genotypes which varied widely for final leaf numbers (14-24) indicated that early flowering in some landraces was almost exclusively due to earlier floral initiation

A comparison of leaf appearance rates among teosinte, maize landraces and modern maize

The rate at which successive new leaves emerge at the stem apex in gramineae (phyllochron) is largely controlled by temperature. Utilizing genetic variation for the phyllochron may be a way to alter plants' responses to the environment or to manipulate time to maturity. Little is known about possible genetic variation in the phyllochron among maize landraces, its ancestor teosinte and modern maize. Controlled environment (phytotron) and field studies were conducted to investigate possible genetic variation for the phyllochron among seven maize (Zea mays) landraces (Apachito, Chapalote, Conico, Tabloncillo, Tehua, Tuxpeno, and Zapalote Chico) sampled from the center of maize diversity in Mexico, a modern US maize hybrid (B73 x Mo17), and two teosintes (Zea diploperennis and Z. mays ssp. parviglumis). In the phytotron the phyllochron was determined for three day/night temperature regimes (22/18, 27/21 and 33/25°C) under a 12 h photoperiod. Genetic variation for the phyllochron among the genotypes was observed in the phytotron and field, however, it was small with extreme values of about +/-15% of the mean. A generally similar phyllochron for modern maize and its wild relatives suggested that this trait has been conserved despite thousands of years of human and natural selection. A similar leaf development rate among genotypes which varied widely for final leaf numbers (14-24) indicated that early flowering in some landraces was almost exclusively due to earlier floral initiation

Three doses of BNT162b2 vaccine confer neutralising antibody capacity against the SARS-CoV-2 Omicron variant.

We report the levels of neutralising antibodies against Wuhan, Delta and Omicron variants in unimmunized infected (group 1), immunised and boosted (group 2) and infected immunised and boosted (group 3) adult individuals. Our observations support the rapid administration of a booster vaccine dose to prevent infection and disease caused by&nbsp;Omicron.</p

Características morfogênicas e estruturais e produção de forragem do capim-marandu submetido a intensidades e freqüências de desfolhação Morphogenetic and structural traits and herbage production of marandugrass under intensities and frequencies of defoliation

Este trabalho foi realizado com o objetivo de avaliar a influência de intensidades (10 e 20 cm) e freqüências de desfolhação (três intervalos de cortes, definidos pelo aparecimento de 5, 7 e 9 folhas/perfilho após cada evento de desfolhação) nas características morfogênicas e estruturais, no perfilhamento e na produção de forragem de Brachiaria brizantha (A. Rich.) Stapf cv. Marandu. Foi utilizado um arranjo fatorial 2 x 3 seguindo um delineamento inteiramente casualizado, com três repetições, totalizando 18 unidades experimentais. Foram realizados dois cortes no tratamento com maior freqüência de desfolhação e um corte nos demais. A maior intensidade de desfolhação proporcionou maior renovação de tecidos foliares, que, aliada a maiores freqüências de desfolhação, condicionou ao dossel perfilhos mais jovens, que se desenvolveram em ambiente com menos competição por luz. A menor intensidade de desfolhação favoreceu a passagem dos perfilhos da fase vegetativa para a reprodutiva, promovendo maior contribuição de pseudocolmo e material morto para a forragem produzida. Em situações em que são utilizadas maiores freqüências de desfolhação, recomenda-se a utilização da intensidade de corte de 10 cm. Quando utilizadas menores freqüências de desfolhação, o corte a 10 cm pode promover a redução na quantidade de forragem produzida, principalmente na freqüência de sete folhas. As maiores freqüências de desfolhação foram as que apresentaram a maior renovação do dossel, com maiores taxas de alongamento e aparecimento de folhas, maior comprimento de lâmina foliar e menor acúmulo e alongamento de pseudocolmo. Apesar da elevada quantidade de forragem produzida no corte a 20 cm e com a freqüência de sete folhas, considerando-se as características morfogênicas e estruturais, o perfilhamento e o acúmulo de forragem, os cortes mais freqüentes ocasionam, além de alta renovação de tecidos, elevada produção de forragem com grande quantidade de folhas e menor quantidade de pseudocolmo e material morto, condicionando melhor eficiência na produção de forragem.<br>This trial was carried out to evaluate the influence of defoliation intensities (10 and 20 cm stubble height) and defoliation frequencies (three cut intervals based on the appearance of 5, 7 and 9 leaves/tiller after each defoliation event) on the morphogenetic and structural traits, tillering and herbage production of Brachiaria brizantha cv Marandu swards. Treatments were allocated to experimental units according to a completely randomized design, in a 2 x 3 factorial arrangement, with three replications, in a total of 18 experimental units. Two cuts were performed in the most frequent treatment and one cut for the remaining treatments. Greater defoliation intensity resulted in greater leaf tissue turn over and, when combined to greater defoliation frequencies resulted in younger tillers, which grew up in an environment with lesser light competition. Cutting intensity at 20 cm favored tiller transition from vegetative to reproductive stage, resulting in greater contribution of pseudo stem and dead material to the herbage mass. If frequent defoliation is used, the 10 cm stubble height is the recommended intensity. If less frequent defoliation is used, the 10 cm stubble height may decrease herbage yield, mainly when using the seven leaves frequency. Greater defoliation frequencies showed greater sward renovation, with greater leaf elongation and leaf appearance rates, greater leaf blade length and lesser pseudo-stem accumulation and elongation. Although greater herbage production was obtained at the 20 cm cutting height and 7 leaves frequency, considering all evaluated traits, more frequent cuts promoted greater tissue turn over with high herbage production characterized by its high amount of leaves and less amount of pseudo stem and dead material, allowing for higher herbage production efficiency

Morphogenetic and structural characteristics of guinea grass tillers at different ages under intermittent stocking

The objective of this research was to assess morphogenetic and structural characteristics of tillers of guinea grass cv. Tanzania at different ages. The pastures of guinea grass were managed in six pasture conditions related to the combination of three frequencies (90, 95, and 99% light interception) and two post-grazing heights (25 and 50 cm). In these six pastures conditions, three tiller ages were evaluated (young, mature, and old). The design was of completely randomized block with three replications. Young tillers exhibited higher leaf appearance rate and leaf elongation rate and, consequently, higher final leaf length and number of live leaves than mature and old tillers, regardless of the pasture condition. On pastures managed with 90 or 95% light interception associated with a post-grazing height of 25 cm, old tillers presented longer leaf lifespan than young and mature ones. There is a progressive reduction in the vigor of growth of pastures of guinea grass cv. Tanzania with advancing tiller age