Laboratory Report

By: Robert D Raabe

Robert D Raabe is Professor Emeritus of Plant Pathology at University of California, Berkeley. He introduced a faster method of…

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A Hot One

A new habañero pepper, named ‘TigerPaw-NR’ has been developed in South Carolina. It was so named because a photograph of the pepper made it look like a tiger’s paw. Not only is it the hottest habañero developed by the Agricultural Research Service, but it is highly resistant to many important species of root knot nematodes. How hot? The Scoville scale measures pepper heat in terms of the amount of capsaicin, the compound that produces the burning sensation. On this scale, jalapeños are in the 3,500 to 5,000 range, habañeros rate 100,000 and higher, and ‘TigerPaw-NR’ rates 348,634. Agricultural Research 55 (6): 22.

More Heat!

Pepper researchers in New Mexico have been experimenting with a chili pepper identified as Capsicum chinense ‘Bhut Solokia’. Plants of this species are known to be the hottest of the chili peppers. The seed of this cultivar was originally collected in India and was sent to the Chili Pepper Institute in 2001. The seed was of poor quality, and it was 2004 before enough seed was available for experimentation. When tested on the Scoville scale, the pepper rated 1,001,304. In studying the true identity using DNA markers, the species for this cultivar was identified as C. chinense, but there was some genetic introgression from C. frutescens. A naturally occurring, interspecific hybrid between the two species kept naturally backcrossing to C. chinense, which accounts for the small amount of C. frutescens DNA in ‘Bhut Solokia’. Hort Science 42:222-224.

A New Menace

First identified in the Western Hemisphere three years ago, red palm mite (Raviella indica) is rapidly spreading through the Caribbean islands, where it attacks many palms, including both ornamental species and coconut palms (Cocos nucifera); forecasts indicate that the mite will cause a fifty percent reduction in the yield of coconuts. It also infests bananas and Heliconia. The mite is extremely prolific: it was estimated that there were between thirty and one hundred million mites on one palm. In addition, the mites are easily transported on the wind to other plants in the area. The mite does not feed on plant epidermis, as do most mites, but, instead, on the inner tissues of the leaves where it causes great damage. In a joint venture between the agriculture departments of the islands and the USDA at Beltsville, an unusual control is being tested. DNA from the mites is first sequenced. Mite predators from the area are then collected and the contents of their guts checked for red mite DNA. Those testing positive are then raised in large numbers so that they can be released where the mites are prevalent. Agricultural Research 55 (4): 4-6.

Corrected Terms

The words pollinator and pollenizer are sometimes used interchangeably, though they have different meanings. A pollinator is an agent (insect, bird, bat, humans, wind) that transfers pollen from where it is produced to the area where it should be placed. A pollenizer is a plant that produces pollen. Horticulture 104 (5): 11.

No Black Pots

In Australia, horticulturists decided to do something about the effects of growing eucalyptus in black containers, which were believed to absorb excessive amounts of heat, resulting in damaged roots. To avoid this, they started growing them in white aggregate bags made of polypropylene, which is sometimes used in making sandbags. Not only were the roots healthier, but they grew vertically rather than in a circular pattern. This was thought to be caused by small amounts of light getting through the white containers and triggering both a geotropic and phototropic response, the latter causing the roots to grow away from the light. A nurseryman has taken the principle, improved the pots, and sells them commercially; for some reason, they are not yet available in the US. The Horticulturist 15 (4): 6-7.

Date Facts

Commercial dates are thought to be the world’s oldest cultivated fruits. Fossil records show that date palms were common in the Mediterranean area and in Mesopotamia fifty million years ago. Written records from about 2,500 BC mention it as a cultivated tree. Date palms grow best between 15° and 25° north latitude, in arid areas of North Africa, the Arabian Peninsula, and southern Iraq. It is estimated that, of the ninety million date palms in the world, sixty-four million grow in the Arab countries. There are approximately 600 cultivars, and the total annual harvest exceeds three million tons. Date palms are dioecious; it takes only one male to pollinate fifty females. Plants are grown from offshoots because, like most fruit trees, dates from seedling trees are not as good as those from trees propagated vegetatively from good stock. About 400 cultivars have been grown in the US, in Florida, Texas, Arizona, and California, but most are grown in the Coachella Valley in Southern California. They were first introduced into that area early in the 1900s by the USDA, which still has an experimental station there. It is estimated that, in the valley, there are a quarter million trees, producing ninety-five percent of the annual US crop. About nine cultivars are grown commercially, but by far the most common is the ‘Deglet Noor’, which means “date of light” or “translucent one;” the seed can be seen inside the fruit. An average tree will produce one hundred pounds of dates per year, but an exceptional one may produce 250 pounds. By far the ultimate in taste is the ‘Khalsah’, but it does not ship well, so is rarely grown and few have had the pleasure of tasting this delicacy. Saudi Aramco World 55 (4):2-8.

Robert D Raabe is a plant pathologist, now retired after more than thirty years of teaching at UC Berkeley, where he continues his research.