Leaf Area Estimation in Chamomile

The knowledge of the variables specific leaf area and leaf area index is important for direct or indirect quantification of plant growth, development and yield. However, there is a lack of these information due to the difficulty in measuring the leaf area of chamomile. Measuring leaf area by direct methods, such as the use of leaf area integrator is a very laborious and time consuming activity because the plant has many leaves and with small size. The use of leaf dry matter is a promising variable for the leaf area estimation. As an important measure to evaluate plant growth, the present study aimed to obtain a model for chamomile leaf area estimation through leaf dry matter. The experiment was conducted in two sowing dates (March 18 and June 30, 2017) at different plant densities (66, 33, 22, 16, 13, 11 and 8 plants m). The leaves of chamomile plants were collected in the plant vegetative and reproductive phases. The leaf area determination was performed using the electronic integration method of leaf area. The specific leaf area was 133 cm g, with no differences between sowing dates, plant densities and phenological phases of plant collection. The leaf area measured with the electronic leaf area integrator exhibited high correlation with chamomile leaf dry matter and the resulting model of leaf area data by the integrator presented optimum performance. This model is indicated for leaf area determination of chamomile when there is availability of leaf dry matter data.


Introduction
Among the medicinal plants grown in Brazil, chamomile (Chamomilla recutita L.) is the most prominent (Corrêa, Júnior, & Scheffer, 2014).Besides the medicinal use, chamomile can also be used for the ornamentation and aromatization of environments and cosmetic purposes.
Growing demand for medicinal plants is observed with increased interest of the population in natural therapies through the use of medicinal plants and herbal products (Borsato et al., 2008).Consequently, this demand requires increments in crop production and yield.Thus, the research development that eases the compression of plant development and which are the factors that potentiate its productivity becomes paramount with greater requirements for medicinal products in the market.Information on specific leaf area (SLA) and leaf area index (LAI) are important for the quantification of growth, development, yield and its estimation through mechanistic modeling.
The SLA is characterized as the ratio between the light-catching surface of a leaf per unit of dry matter investment.Moreover, it is an important variable for the measurement of stresses that occur throughout the plant cycle and can be indirectly associated with the leaf useful life.Low SLA species invest more dry matter per leaf and often have low relative growth and net photosynthesis rates but have longer leaf longevity.Meanwhile, high SLA species invest less dry matter per leaf, growing rapidly and with shorter development cycle (Reich et al., 1992).However, the interception of solar radiation is directly conditioned by the LAI and the architecture of the plant canopy elements.Moreover, the photosynthetic process depends not only on the interception of light energy but also on the plant efficiency in its conversion into chemical energy (Taiz & Zeiger, 2013).
Accurate LAI measurements are necessary to monitor the changes occurring in the plant throughout the development cycle and their relationship with the different biotic and abiotic factors.Therefore, this knowledge is especially useful with regard to the crop phytosanitary management.The knowledge of the leaf area is essential, considering that the LAI is the relation between the leaf area and the soil area occupied by the crop.There are many direct and indirect methods of measuring and/or estimating the plant leaf area.Measurements are taken directly on the leaf in direct methods.In the indirect methods, one determinant variable for the measured leaf area is used and significant correlation and models of estimation can be established.The leaf size, leaf disk and electronic leaf area integrators are among the most used and conventional methods for the leaf area determination.
Besides having many small leaves with less than five centimeters, chamomile has pinned leaves with linear segments, which hampers their measurement through the leaf dimensions.The measurement by the use of leaf area integrator has little use because it is an expensive and time-consuming activity.Another disadvantage is the high acquisition cost of the apparatus.
A simpler and faster alternative is the use of leaf dry matter to estimate leaf area, as performed for cotton by Monteiro et al. (2005) and cashew, soybeans and corn by Ramos et al. (2015), presenting generally stable coefficients.As leaf area is an important measure to evaluate plant growth, the present study aimed to obtain a model for chamomile leaf area estimation through leaf dry matter.

Method
One experiment with chamomile were carried out in an experimental area located at lat 29°43′23″ S, long 53°43′15″ W and 95 m of altitude during the agricultural year of 2017.According to the Köppen climate classification, the climate of the region is Cfa fundamental type, characterized as humid subtropical with hot summer and normal rainfall distributed uniformly during the four seasons of the year, with an annual mean of 1,712 mm (Heldwein et al., 2009).The soil of the experimental area is classified as "Argissolo Vermelho Distrófico arênico" Paleudalf (Santos et al., 2013).
The sowing procedure of the experiments occurred on March 18 and June 30, 2017, using the cultivar Mandirituba, with seeds obtained from growers in the municipality of Mandirituba-PR.Sowing was carried out in rows, after previous plowing and harrowing of the area, aiming to provide better initial plant development conditions.The fertilization was performed based on the soil analysis and the chamomile crop requirements (CQFS-RS/SC, 2004).The only cultural treatment performed was manual weeding, which was carried out throughout the crop cycle in order to avoid damage caused by weed competition.There was no incidence of pests and diseases during the experiment, requiring no control interventions.Complementary irrigation was performed by dripping in the experimental area in order to avoid the influence of water deficit stress on chamomile crop development.
After plant emergence, thinning was carried out in the two areas with the aim of applying the treatments of different plant densities.The adopted spacing was 30 cm between rows and 5, 10, 15, 20, 25, 30 and 40 cm between plants, totaling the plant densities of 66,33,22,16,13,11, and 8 plants m -2 , respectively.In each experimental area, the seven plant densities were allocated with four replicates, totaling 28 experimental units per sowing date.Each experimental unit consisted of 10 rows of plants with dimensions of 3 × 3 m, covering a total area of 9.0 m 2 and a useful area of 4 m 2 .
For the leaf area analyzes, six collects were taken in each sowing date and two plants per plot were collected at each evaluation.Furthermore, the six collects were divided in three during the vegetative phase and the other three in the reproductive phase.
The experiment was arranged in a trifactorial scheme, using a completely randomized design with four replicates.The factor A was composed by the sowing dates (March 18 and June 30, 2017), the factor B by the seven different plant densities (66,33,22,16,13,11 and 8 plants m -2 ) and the factor C by the plant development stages (vegetative and reproductive).Therefore, a total of 336 chamomile plants were collected for the analysis of leaf area and its relation with the leaf dry matter.
Leaves were removed from the plants after the collection and the number of leaves of each analyzed sample per plant ranged from ten to all plant leaves.Thereby, the leaves of each sample were randomly taken from the plant, with different sizes and locations in the plant.Leaf area determination was performed using the electronic integration method of leaf area.
The leaf area integrator Li-3000 model from Liquor was used for leaf area measurement.Each leaf was individually passed through the electronic sensor of rectangular approximation, which provides a resolution of 1 mm 2 .After leaf area determination of the chamomile leaves, the leaf samples of each plant were conditioned in paper bags and dried in a 60 °C ventilated oven until the samples obtained constant weight.Subsequently, the jas.ccsenet.

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Results
The value method did factors (so (Table 1

Conclusions
The chamomile specific leaf area did not differ between sowing dates, plant densities and phenological phases of plant collection.The specific leaf area of chamomile was 133 cm 2 g -1 .
The leaf area measured by the electronic integrator exhibited high correlation with the chamomile leaf dry matter.
The model resulting from leaf area data measured by the electronic integrator presented optimum performance, being indicated for the chamomile leaf area determination when there is available leaf dry matter data.