Theobroma cacao L. cultivar CCN 51: a comprehensive review on origin, genetics, sensory properties, production dynamics, and physiological aspects

Many decades of improvement in cacao have aided to obtain cultivars with characteristics of tolerance to diseases, adaptability to different edaphoclimatic conditions, and higher yields. In Ecuador, as a result of several breeding programs, the clone CCN 51 was obtained, which gradually expanded through the cacao-production regions of Ecuador, Colombia, Brazil and Peru. Recognized for its high yield and adaptability to different regions and environments, it has become one of the most popular clones for breeding programs and cultivation around the world. This review aims to summarize the current evidence on the origin, genetics, morphological, volatile compounds, and organoleptic characteristics of this clone. Physiological evidence, production dynamics, and floral biology are also included to explain the high yield of CCN 51. Thus, characteristics such as osmotic adjustment, long pollen longevity, and fruit formation are further discussed and associated with high production at the end of the dry period. Finally, the impact of this popular clone on the current and future cacao industry will be discussed highlighting the major challenges for flavor enhancement and its relevance as a platform for the identification of novel genetic markers for cultivar improvement in breeding programs.

Impact of Storage Temperature on Pollen Viability and Germinability of Four Serbian Autochthon Apple Cultivars

Globalization has drastically reduced the number of autochthon apple cultivars in the Serbian market and most of them have nearly disappeared; however, some of these cultivars, such as Petrovača, Budimka, Kolačara Pozna, and Kožara, have extraordinary quality, good pomological characteristics, and pest and disease resistance. The present study was conducted to develop a protocol for the storage of pollen for further use in the conservation and breeding of these cultivars. Viability and germination of the mature pollen were tested in vitro, at four storage temperatures (20, 4, −20, and −80°C), right after harvest or 1, 2, 3, 4, 5, and 6 months after storage. Differences in fresh pollen viability and germination between cultivars were statistically significant and ranged from 60 to 88% and 59 to 98%, respectively. Fresh pollen of cv. Budimka showed the highest viability and germination in comparison with other cultivars, especially cv. Kožara. Pollen viability and germination decreased over the storage period, and it was the lowest after 6 months of storage at room temperature in all tested cultivars. Storage at 4°C prolonged the pollen viability and germinability of 1–5 fold, depending on the cultivar and treatment duration; however, the pollen longevity of all cultivars was significantly extended when stored at −20 or −80°C. After 6 months, pollen of cv. Budimka stored at −20 and −80°C showed 14–15 fold higher germination rates in relation to pollen storage at room temperature for the same period. The results of the present study suggest that the pollen of these apple cultivars could be efficiently maintained at −20°C and could be further used for breeding purposes, e.g., for crossings between cultivars that flower at different times of the year.

First Steps in the Successful Fertilization of Rice and Arabidopsis: Pollen Longevity, Adhesion and Hydration

Understanding the behavior of pollen during pollination is important for food security in the future. The elucidation of pollen development and growth regulation largely relies on the study of the dicotyledonous model plant Arabidopsis thaliana. However, rice (Oryza sativa) pollen exhibits different characteristics to that of Arabidopsis. The latter undergoes programmed dehydration and withstands adverse environmental conditions, whereas rice pollen is sensitive to desiccation. Moreover, the short longevity of rice pollen significantly hampers hybrid seed production. Although the “omics” data for mature rice pollen have been accumulated, few genes that control pollination and pollen hydration have been identified. Therefore, to facilitate future studies, it is necessary to summarize the developmental processes involved in pollen production in rice and to consolidate the underlying mechanisms discovered in previous studies. In this review, we describe the pollen developmental processes and introduce gametophytic mutants, which form defective pollen in Arabidopsis and rice. In addition, we discuss the perspectives on the research on pollen longevity, adhesion and hydration.

Pollen Biology and Dispersal Dynamics in Waterhemp (Amaranthustuberculatus)

Waterhemp is a major weed of field crops in the Midwestern United States. Its prevalence is at least partly due to its rapid evolution of resistance to many groups of herbicides over the last two decades. In light of its dioecy and anemophily, pollen movement in waterhemp is considered to be an important factor in the spread of herbicide resistance genes. Thus, the biology and dispersal profile of waterhemp pollen are critical determinants for understanding and predicting the spatial population dynamics of herbicide resistance in this species. In this study, pollen longevity was investigated with greenhouse experiments, and pollen dispersal and the effect of pollen competition were investigated in field plots. Pollen dispersal was determined by measuring the frequency of seeds produced on receptor plants positioned at various distances from a pollen source, which flowered in synchrony with the receptor plants. Results indicated that waterhemp pollen can remain viable up to 120 h, implying a low limitation of pollen dispersal by its longevity. Effective pollen dispersal declined exponentially with distance, with most pollen fertilizing recipient plants within 50 m of the pollen source. However, long distance pollen dispersal (800 m) was also observed. We also saw evidence for pollen swamping in this species. Under conditions of pollen competition among distinct genotypes, pollination success was inversely related to distance between pollen donors and receptors. However, relative pollen density may also play an important role in determining the rate of long distance gene flow. This study confirmed the potential of waterhemp pollen to effect long distance gene flow and provides supporting data for quantitative spatial modeling of waterhemp resistance dynamics.

Pollen Biology of Robinia pseudoacacia on Zhen Mountain in Yantai

The pollen–ovule ratios, pollen fertility rate, pollen viability and longevity, pollen histochemistry of Robinia pseudoacacia flowers were determined in the field on Zhen Mountain in Yantai, Shandong province in China. The main results were as follows: Robinia pseudoacacia is completely fertile and has starchy pollen. The pollen longevity was about 80h. The pollen viability was higher than 90% at the beginning of anthesis on sunny days. 80h later, most pollen grains lose their viability. Pollen–ovule ratio (P/O) is 192±19. Accoring to Cruden, R. pseudoacacia is facultative autogamous.

Pollen Biology of Calligonum mongolicum in the Middle Reaches of Heihe River

The pollen–ovule ratios, pollen fertility rate, pollen viability and longevity, pollen histochemistry of Calligonum mongolicum flowers were determined in the field by the middle reaches of Heihe River. The main results were as follows: Calligonum mongolicum is completely fertile and has starchy pollen. Anthers matured heterotypically. The pollen longevity was about 10h. The pollen viability was higher than 70% at the beginning of anthesis on sunny days. No difference in the pollen production of single anther was found between different flower morphes, but significant difference was in that of single flower. The pollen-ovule ratios of different morph flowers were 1625±125, 1750±177, 1500±102, 1563±120, 1875±72. Pollen–ovule ratios (P/O) reveal that C. mongolicum is facultative autogamous.